1. Ch. 11: Gene regulations How is cloning possible?
Every cell has the same chromosomes
Then….. Why does a heart muscle cell look different from a skin cell?
Organisms respond to their environment by altering gene expression
Central question: what regulates gene expression?

2. Differentiation
Differentiation is controlled by turning specific sets of genes on or off
For the BLAST Animation Signaling Across Membranes, go to Animation and Video Files.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type.

3. DNA Packing eukaryotic chromosomes condense during prophase of Mitosis
eukaryotic chromosomes condense during prophase of Mitosis
helps regulate gene expression by preventing transcription
Nucleosomes
Tight helical fiber =
Supercoil = coiling of the tight helical fiber
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
2. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.

4. Animation: DNA Packing
Metaphase
chromosome
Tight helical fiber
(30-nm diameter)
DNA double helix
(2-nm diameter)
Linker
“Beads on
a string”
Nucleosome
(10-nm
diameter)
Histones
Figure 11.3 DNA packing in a eukaryotic chromosome.
This figure shows the increasing levels of DNA packing. The initial level of the nucleosome involves ~140 base pairs of DNA surrounding 8 molecules of histone proteins. A linker region of 40–60 nucleotides is found between nucleosomes. Histones are highly evolutionarily conserved proteins, with only two amino acid changes between histone H4 molecules in pea plants and cows. The combination of histones with DNA has long been associated with the inhibition of transcription. Histones have sites for acetylation in their amino-terminal regions that can reduce binding between positively charged lysine residues and negatively charged DNA. Histone acetylation has been correlated with increased transcriptional activity as it would allow for transient removal of the histone-protein portion of the nucleosome during transcription.
Supercoil
(300-nm diameter)
700 nm
Animation: DNA Packing

5. X-chromosome inactivation
female mammals
one of the two X chromosomes is highly compacted and transcriptionally inactive (Barr body)
Occurs early in embryonic development, thus all cellular descendants have the same inactivated chromosome
Tortoiseshell fur coloration is due to inactivation of X chromosomes in heterozygous female cats
Human athletes are tested for the presence of a Barr body to be sure they are appropriately competing as males and females.
The number of Barr bodies is equal to the number of X chromosomes minus 1.
Related to Module 8.22, females with Turner syndrome will have 0 Barr bodies and males with Klinefelter syndrome will have 1 Barr body.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.

6. Early embryo Two cell populations in adult Cell division and random
Early embryo
Two cell populations
in adult
Cell division
and random
X chromosome
inactivation
Active X
Orange
fur
X chromosomes
Inactive X
Inactive X
Allele for
orange fur
Figure 11.4 Tortoiseshell pattern on a cat, a result of X chromosome inactivation.
Alternative inactivation of X chromosomes can produce patches of black and orange fur in a female cat heterozygous for these two alleles.
Can a male cat show the tortoiseshell phenotype? Yes, if he has an XXY chromosome composition!
Active X
Black fur
Allele for
black fur

7. Eukaryotic gene expression
Each gene has its own promoter and terminator
Are controlled by interactions between numerous regulatory proteins and control sequences
It is useful to compare gene organization in eukaryotes to prokaryotes, where genes are found in operons so that a cluster of genes is under the control of the same promoter and terminator. Many genes in prokaryotes are continually active and are only switched off in response to environmental circumstances. Prokaryotic genes have repressors and activators as regulatory proteins and promoters and operators as control sequences, but this represents a smaller array of control elements than found in eukaryotic nuclei.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. The authors note that the selective unpackaging of chromosomes is the “course adjustment” of eukaryotic gene expression. The initiation of RNA synthesis is the fine-tuning of the regulation. If you have recently asked your students to use microscopes in lab, you might relate these degrees of adjustment to the coarse and fine control knobs of a microscope.

8. Animation: Initiation of Transcription
Regulatory proteins
Transcription factors - help RNA polymerase bind to the promoter
Activators –
Silencers -
Control sequences
Promoter
Enhancer
Related genes located on different chromosomes can be controlled by similar enhancer sequences
Enhancer sequences can be located either upstream or downstream from the promoter. They can be found in close proximity or at great distances from the promoter region. Sequences called insulators can be positioned between an enhancer and a promoter to prevent enhancer action on that promoter.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. The authors note that the selective unpackaging of chromosomes is the “course adjustment” of eukaryotic gene expression. The initiation of RNA synthesis is the fine-tuning of the regulation. If you have recently asked your students to use microscopes in lab, you might relate these degrees of adjustment to the coarse and fine control knobs of a microscope.
Animation: Initiation of Transcription

9. Enhancers Promoter Gene DNA Activator proteins Transcription factors
Gene
DNA
Activator
proteins
Transcription
factors
Other
proteins
RNA polymerase
Figure 11.5 A model for the turning on of a eukaryotic gene.
Sequence of events:
Activator proteins bind to an enhancer sequence.
DNA bends to bring the enhancer sequence closer to the promoter region.
Activators interact with other transcription factors that bind to the promoter.
RNA polymerase is properly positioned on the promoter and transcription is initiated.
Bending
of DNA
Transcription

10. Alternative RNA splicing
Can involve removal of an exon with the introns on either side
Modes of alternative splicing can include exon skipping (as shown in Figure 11.6), intron retention, or the use of an alternative splice donor or acceptor site located within an exon region.
Some diseases are caused by mutations that promote alternative splicing. For example, one form of -thalassemia is due to mutations in exons 1 and 2 of the -globin gene that cause aberrant splicing and production of an abnormal hemoglobin chain. The use of small nucleotide chains complementary to the mRNA (antisense oligonucleotides) to block the incorrect splice sites has been demonstrated in cultured human cells, indicating promise as a possible therapy for thalassemia patients.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. Alternative RNA splicing is like remixing music to produce a new song or re-editing a movie for a different effect.
Animation: RNA Processing

11. Exons DNA 1 2 3 4 5 RNA transcript 1 2 3 4 5 RNA splicing or mRNA 1 2
Exons
DNA 1 2 3 4 5
RNA
transcript 1 2 3 4 5
Figure 11.6 Production of two different mRNAs from the same gene.
This figure shows exon skipping, one mode of alternative splicing.
One product contains exon 3 and involved the removal of exon 4 with introns on either side. This splicing start site (5) was on the intron between 3 and 4 and the splicing end site (3) was on the intron between 4 and 5.
The other product contains exon 4 and involved the removal of exon 3 with the introns on either side.
RNA splicing or
mRNA 1 2 3 5 1 2 4 5

12. Small RNAs control gene expression
RNA interference (RNAi)
small, complementary RNAs bind to mRNA transcripts, blocking translation
MicroRNA (miRNA)
MicroRNA + protein complex binds to complementary mRNA transcripts, blocking translation
RNAi involves microRNA and small interfering RNA. Both are transcribed from the genome and form double-stranded structures by folding on themselves. An enzyme called Dicer cuts them into small molecules, and the strands then separate for binding to mRNA.
Low levels of a specific microRNA were shown to be associated with acute myeloid leukemia. Due to a reduction in miR-204, two genes of the Hox group show increased expression. Hox genes are involved in both embryonic development and blood cell development.
In previous views of gene control, the transcription of a gene was paramount. Now the transcription of an inhibitor of mRNA function is also a factor to consider.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. Recent references in older books and outdated websites may characterize DNA that does not code for rRNA, tRNA, or mRNA as junk DNA. The relatively recent discovery of miRNA and its significant roles in gene regulation reveals the danger of concluding that the absence of evidence is evidence of absence!
Animation: Blocking Translation
Animation: mRNA Degradation

13. Protein miRNA miRNA- protein complex Target mRNA mRNA degraded OR
Protein
miRNA 1
miRNA-
protein
complex 2
Target mRNA
Figure 11.7 The mechanism of RNA interference.
This figure shows the steps involved in RNA interference with microRNA.
MicroRNA binds to a large protein complex.
MicroRNA protein complex binds to complementary mRNA.
This triggers mRNA degradation or interferes with translation. 3 4
mRNA degraded OR
Translation blocked

14. Control of gene expression also occurs with Breakdown of mRNA
Control of gene expression also occurs with
Breakdown of mRNA
Initiation of translation
Protein activation
Protein breakdown
Hormones have been shown to cause an increase in the half-lives of specific mRNAs. For example, estrogen was shown to stabilize the mRNA for the estrogen receptor in sheep endometrial tissue. Prolactin caused a 20-fold increase in the half-life of casein mRNA in mammary tissue.
The sequence of reactions in blood clotting shows protein activation through cleavage of amino acids from polypeptide chains. One example is the conversion of prothrombin to thrombin, involving two cleavage reactions. Thrombin is then involved in the activation of fibrinogen to fibrin, which forms the blood clot.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. The authors develop an analogy between the regulation of transcription and the series of water pipes that carry water from your local water supply, perhaps a reservoir, to a faucet in your home. At various points, valves control the flow of water. Similarly, the expression of genes is controlled at many points along the process. Figure 11.9 illustrates the flow of genetic information from a chromosome—a reservoir of genetic information—to an active protein that has been made in the cell’s cytoplasm. The multiple mechanisms that control gene expression are analogous to the control valves in water pipes. In the figure, a possible control knob indicates each gene expression “valve.” In the figure, the large size of the transcription control knob highlights its crucial role.

15. Ex. Insulin formation Folding of polypeptide and formation of
Ex. Insulin formation
Folding of
polypeptide and
formation of
S—S linkages
Cleavage
Initial polypeptide
(inactive)
Folded polypeptide
(inactive)
Active form
of insulin
Figure 11.8 Protein activation: The role of polypeptide cleavage in producing the active insulin protein.
This figure shows the activation of insulin involving cleavage of a long polypeptide chain to form two covalently linked chains.

16. Epigenetic Inheritance
This can be accomplished by acetylation or methylation of histones

17. Regulation of Chromatin Structure
Chemical modification of histone tails can affect the configuration of chromatin and thus gene expression
DNA
double helix
Histone
tails
(a) Histone tails protrude outward from a nucleosome

18. Addition of methyl groups to certain bases in DNA is associated with reduced transcription in some species
(b) Acetylation of histone tails promotes loose chromatin structure that permits transcription
Unacetylated histones
Acetylated histones

19. Figure 11.9 The gene expression “pipeline” in a eukaryotic cell.
NUCLEUS
Chromosome
DNA unpacking
Other changes to DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of cap and tail
Splicing
Tail
mRNA in nucleus
Cap
Flow through
nuclear envelope
mRNA in cytoplasm
CYTOPLASM
Breakdown of mRNA
Broken-
down
mRNA
Translation
Figure 11.9 The gene expression “pipeline” in a eukaryotic cell.
Polypeptide
Cleavage / modification /
activation
Active protein
Breakdown
of protein
Broken-
down
protein

20. Why so much control over gene expression?
It allows cells to respond appropriately to their environment
Signal transduction pathways convert messages received at the cell surface to responses within the cell via gene expression
Three steps:
Reception –
Amplification/transduction –
Response - transcription factor is activated, enters nucleus, transcribes specific genes
An increase in cell division is one example of a cellular response at the end of a signal transduction pathway. Epidermal growth factor (EGF) is a signal molecule that leads to an increase in the activity of transcription factor NF-kappaB. NF-kappaB increases transcription of the gene for cyclin D1. Cyclin D1 promotes progress through the cell cycle at the G1 S transition, through deactivation of retinoblastoma (Rb) protein. This pathway leads to the uncontrolled growth of estrogen-receptor negative (ER-negative) breast cancer cells. ER-negative cells have higher levels of EGF receptors and thus produce elevated levels of NF-kappaB and cyclin D1. The possibility of inhibiting the action of NF-kappaB as a cancer therapy is being pursued.
Student Misconceptions and Concerns
1. The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation.
2. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.9 can be a helpful reference to organize the potential sites of regulation.
Teaching Tips
1. The action of an extracellular signal reaching a cell’s surface in a signal transduction pathway is like pushing the doorbell at a home. The signal is converted to another form (pushing a button rings a bell), and activities change within the house as someone comes to answer the door.
2. Some of the stages of a signal transduction pathway can be compared to a human reaction. Consider someone calling your name. (1) Reception—The sound waves of someone’s voice hitting and changing the shape of your eardrum. (2) Transduction—Your ear converts sound waves to nerve impulses and sends a signal to your brain that your name has been called. (3) Response—You look around to see who is calling.

21. Signaling cell Signaling molecule Plasma membrane Receptor protein
Signaling
molecule
Plasma
membrane 1
Receptor
protein 2 3
Target cell
Relay
proteins
Transcription
factor
(activated) 4
Nucleus
Figure A signal transduction pathway that turns on a gene.
This figure represents a signal transduction pathway that leads to transcription of a specific gene to promote a cellular response.
DNA 5
Transcription
mRNA
New
protein 6
Translation

22. Cloning: How? Nuclear transplantation
Cloning: How? Nuclear transplantation
Replacing the nucleus of an egg cell with a nucleus from an adult somatic cell. Allow embryo to form. Embryo can be used in:
Reproductive cloning
Therapeutic cloning
Grow embryonic stem cells in culture
Induce stem cells to differentiate and grow into organs, tissues, etc.
Since nuclear transplantation requires both an egg and nuclear donor, the resulting cloned animal may have differences in mitochondrial genes, as these are derived from the egg donor.
While nuclear changes related to differentiation were successfully reversed in producing Dolly, the chromosomes she received retained a significant characteristic from the donor adult that may have shortened her lifespan. These chromosomes were reduced in size, having lost DNA at the ends, or telomeres. The telomeres tend to shorten over successive cell divisions, as lagging strand synthesis may not be completed during DNA replication. Telomeres are repeated sequences that do not carry genes, but the loss can continue into the adjacent gene regions. Shortening of telomeres has been related to aging and to limiting of cell division. Dolly lived to about half her full life expectancy, contracting a contagious lung disease caused by a virus. It has been proposed that the shorter length of her chromosomes may have contributed to her reduced lifespan.
For the Discovery Video Cloning, go to Animation and Video Files.
For the BLAST Animation Stem Cells, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Students often fail to see the similarities between identical twins and cloning. Each process produces multiple individuals with identical nuclear genetic material.
2. Students often assume that clones will appear and act identically. This misunderstanding provides an opportunity to discuss the important influence of the environment in shaping the final phenotype.
Teaching Tips
1. The researchers that cloned Dolly the sheep from a mammary gland cell named Dolly after the celebrity country singer Dolly Parton.
2. Preimplantation genetic diagnosis (PGD) is a genetic screening technique that removes one or two cells from an embryo at about the 6- to 10-cell stage. The= cells that are removed are genetically analyzed while the remaining embryonic cell mass retains the potential to develop. This technique permits embryos to be genetically screened before implanting them into a woman. However, PGD has another potential use. Researchers can use PGD to obtain embryonic stem cells without destroying a human embryo. This procedure might be more acceptable than methods that destroy the embryo to obtain embryonic stem cells.

23. Donor cell Nucleus from donor cell Reproductive cloning
Donor
cell
Nucleus from
donor cell
Reproductive
cloning
Implant blastocyst in
surrogate mother
Clone of
donor is born
Remove
nucleus
from egg
cell
Add somatic cell
from adult donor
Grow in culture
to produce an
early embryo
(blastocyst)
Therapeutic
cloning
Remove embryonic
stem cells from
blastocyst and
grow in culture
Induce stem
cells to form
specialized cells
Figure Nuclear transplantation for cloning.
This figure distinguishes between reproductive and therapeutic cloning.

24. To clone or not to clone….
Benefits of reproductive cloning?
Disadvantages of cloning?
Student Misconceptions and Concerns
1. Students often fail to see the similarities between identical twins and cloning. Each process produces multiple individuals with identical nuclear genetic material.
2. Students often assume that clones will appear and act identically. This misunderstanding provides an opportunity to discuss the important influence of the environment in shaping the final phenotype.
Teaching Tips
1. Preimplantation genetic diagnosis (PGD) is a genetic screening technique that removes one or two cells from an embryo at about the 6- to 10-cell stage. The= cells that are removed are genetically analyzed while the remaining embryonic cell mass retains the potential to develop. This technique permits embryos to be genetically screened before implanting them into a woman. However, PGD has another potential use. Researchers can use PGD to obtain embryonic stem cells without destroying a human embryo. This procedure might be more acceptable than methods that destroy the embryo to obtain embryonic stem cells.
2. Students might not immediately understand why reproductive cloning is necessary to transmit specific traits in farm animals. They may fail to realize that unlike cloning, sexual reproduction mixes the genetic material and may not produce offspring with the desired trait(s).
3. The transplantation of pig or other nonhuman tissues into humans (called xenotransplantation) risks the introduction of pig (or other animal) viruses into humans. This viral DNA might not otherwise have the capacity for transmission to humans.

25. Human stem cell research
Ethical concerns with reproductive cloning
Ethical concerns with therapeutic cloning?
Benefits:
Human embryos – have the greatest potential to give rise to all cell types
Adult stem cells (bone marrow) or cord blood cells
can give rise to many but not all types of cells
Student Misconceptions and Concerns
1. Students often fail to see the similarities between identical twins and cloning. Each process produces multiple individuals with identical nuclear genetic material.
2. Students often assume that clones will appear and act identically. This misunderstanding provides an opportunity to discuss the important influence of the environment in shaping the final phenotype.
Teaching Tips
1. Preimplantation genetic diagnosis (PGD) is a genetic screening technique that removes one or two cells from an embryo at about the 6- to 10-cell stage. The= cells that are removed are genetically analyzed while the remaining embryonic cell mass retains the potential to develop. This technique permits embryos to be genetically screened before implanting them into a woman. However, PGD has another potential use. Researchers can use PGD to obtain embryonic stem cells without destroying a human embryo. This procedure might be more acceptable than methods that destroy the embryo to obtain embryonic stem cells.
2. The political restrictions on the use of federal funds to study stem cells illustrate the influence of society on the directions of science. As time permits, consider opportunities to discuss or investigate this and other ways that science and society interact.

26. Ch 12: DNA Technology DNA profiling
Genetically modified organisms/recombinant DNA technology
Gene therapy
Genomics

27. Amplify (copy) markers for analysis –
1. DNA profiling = analysis of DNA fragments to determine whether they come from a particular individual
3 steps: .
Amplify (copy) markers for analysis –
Compare sizes of amplified fragments by gel electrophoresis
For BLAST Animation DNA Fingerprinting, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Television programs might lead some students to expect DNA profiling to be quick and easy. Ask students to consider why DNA profiling actually takes many days or weeks to complete.
Teaching Tips
1. Figure describes the general steps of DNA profiling. This overview is a useful reference to employ while the details of each step are discussed.

28. 1. Select genetic marker to analyze
Short tandem repeats (STRs) are genetic markers used in DNA profiling
STRs =
STR analysis compares the lengths of STR sequences at specific regions of the genome
Current standard for DNA profiling is to analyze 13 different STR sites
D7S820 represents a region on chromosome 7 that is one of the 13 standard loci used for DNA profiling. Its sequence, GATA, can be repeated from 5 to 16 times. This results in 78 possible genotypes in the population. Sites with large amounts of variation are chosen for DNA profiling to have the greatest chance of distinguishing between individuals. Using more than one location allows a multiplication of the odds of finding two people with the same genotype. As described in Module 12.15, there should be a less than 1 in 10 billion chance that two unrelated individuals share the same profile for the 13 standard STR loci. This depends on the frequencies of the alleles in a specific population. For example, one DNA profiler analyzed his own DNA at the 13 STR sites and calculated that his profile would only be found among 1 in 7.7 quadrillion Caucasian individuals (1 in 7.7 x 1015).
Student Misconceptions and Concerns
1. Television programs might lead some students to expect DNA profiling to be quick and easy. Ask students to consider why DNA profiling actually takes many days or weeks to complete.
2. Students might expect DNA profiling for criminal investigations to involve an analysis of the entire human genome. Consider explaining why such an analysis is unrealistic and unnecessary. Modules 12.12–12.16 describe methods used to describe specific portions of the genome of particular interest.
Teaching Tips
1. In most legal cases, the probability of two people having identical DNA profiles can be one in 10 billion or more. However, eyewitness testimony has been a standard part of the justice system. If you want to make the point about the unreliability of eyewitnesses in a trial, compared to techniques such as genetic profiling, consider this exercise. Arrange for a person who is not well known to the class to run into your classroom, take something you have placed near you (perhaps a bag, stack of papers, or box), and leave quickly. You need to take care that no one in the class is so alarmed as to do something dangerous. Once the “thief” is gone, tell the class that this was planned and do not speak. Have them each write a description of the person, including height, hair color, clothing, facial hair, behavior, etc. Many students will be accurate, but some will likely get details wrong. This is also an effective exercise to demonstrate the need for large sample sizes and accurate recording devices for good scientific technique.

29. STR site 1 STR site 2 Crime scene DNA Number of short tandem
STR site 1
STR site 2
Crime scene DNA
Number of short tandem
repeats match
Number of short tandem
repeats do not match
Suspect’s DNA
Figure 12.14A Two representative STR sites from crime scene DNA samples.
This figure shows differences in the numbers of short tandem repeats that can be used in DNA profiling.

30. 2. Amplify the DNA sample
Polymerase chain reaction (PCR) = method of amplifying a specific segment of a DNA molecule
Relies upon a pair of primers =
Repeated cycle of steps for PCR:
Sample is heated to separate DNA strands
Sample is cooled and primer binds to specific target sequence
Target sequence is copied with DNA polymerase
From one target DNA sequence, 30 cycles of PCR will produce over 1 million copies.
The use of primers is related to the native activity of DNA polymerase. To synthesize a DNA strand, DNA polymerase adds nucleotides to the 3′ end of a short nucleotide strand bound to the template. In the cell, primers are composed of RNA, synthesized by an enzyme called primase. These RNA segments are later removed from the DNA product. In PCR, synthetically produced DNA primers serve as the starting point for the polymerase.
The heat-stable Taq polymerase was isolated from Thermus aquaticus, a bacterium found in hot springs. The enzyme can withstand heating to 94oC and synthesize DNA at 72oC during PCR. This is a helpful illustration of the effect of natural selection in favoring a form of the enzyme that would not denature with the high temperatures of the bacterium’s environment.
Student Misconceptions and Concerns
1. Television programs might lead some students to expect DNA profiling to be quick and easy. Ask students to consider why DNA profiling actually takes many days or weeks to complete.
2. Students might expect DNA profiling for criminal investigations to involve an analysis of the entire human genome. Consider explaining why such an analysis is unrealistic and unnecessary. Modules 12.12–12.16 describe methods used to describe specific portions of the genome of particular interest.
Teaching Tips
1. In PCR, the product becomes another master copy. Imagine that while you are photocopying, every copy is used as a master at another copy machine. This would require many copy machines. However, it would be very productive!

31. Figure 12.12 DNA amplification by PCR.
Cycle 1
yields 2 molecules
Cycle 2
yields 4 molecules
Cycle 3
yields 8 molecules
Genomic
DNA 3 5 3 5 3 5 5 1
Heat to
separate
DNA strands 2
Cool to allow
primers to form
hydrogen bonds
with ends of
target sequences 3
DNA
polymerase adds
nucleotides
to the 3 end
of each primer 3 5 5 3
Target
sequence 5 5 3 5 3 5 3
Figure DNA amplification by PCR.
This figure shows several cycles of the PCR process, emphasizing that the number of templates doubles with each cycle.
Primer
New DNA

32. Video: Biotechnology Lab
3. Gel electrophoresis
separates DNA molecules based on size
DNA samples placed at one end of a porous gel
Current is applied and DNA molecules move from the negative electrode toward the positive electrode
DNA fragments appear as bands, visualized through staining or radioactivity or fluorescence
For BLAST Animation Gel Electrophoresis, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Television programs might lead some students to expect DNA profiling to be quick and easy. Ask students to consider why DNA profiling actually takes many days or weeks to complete.
2. Students might expect DNA profiling for criminal investigations to involve an analysis of the entire human genome. Consider explaining why such an analysis is unrealistic and unnecessary. Modules 12.12–12.16 describe methods used to describe specific portions of the genome of particular interest.
Teaching Tips
1. Separating ink using paper chromatography is a simple experiment that approximates some of what occurs in gel electrophoresis. Consider doing this as a class demonstration while addressing electrophoresis. Cut a large piece of filter paper into a rectangle or square. Use markers to color large dots about 2 cm away from one the edge of the paper. Separate the dots from each other by 3–4 cm. Place the paper on edge, dots down, into a beaker containing about 1 cm of ethanol or isopropyl alcohol (50% or higher will do). The dots should not be in contact with the pool of alcohol in the bottom of the beaker. As the alcohol is drawn up the filter paper by capillary action, the alcohol will dissolve the ink dots. As the alcohol continues up the paper, the ink follows. Not all of the ink components move at the same speed, based upon their size and chemical properties. If you begin the process at the start of class, you should have some degree of separation by the end of a 50-minute period. Experiment with the technique a day or two before class to fine tune the demonstration. (Save and air-dry these samples for your class.) Consider using brown, green, and black markers, since these colors are often made by color combinations.
Video: Biotechnology Lab

33. Mixture of DNA fragments of different sizes Longer (slower) molecules
Mixture of DNA
fragments of
different sizes
Longer
(slower)
molecules
Power
source
Gel
Shorter
(faster)
molecules
Figure Gel electrophoresis of DNA.
Completed gel

34. Crime scene Suspect 1 Suspect 2 DNA isolated DNA of selected
Crime scene
Suspect 1
Suspect 2 1
DNA isolated 2
DNA of selected
markers amplified
Figure An overview of DNA fingerprinting.
This figure shows the process of DNA profiling (also called DNA fingerprinting).
DNA is isolated.
DNA is amplified by polymerase chain reaction (see Module 12.12).
The amplified fragments are compared by agarose gel electrophoresis (see Module 12.13). 3
Amplified DNA
compared

35. Mixture of DNA
fragments
Longer
fragments
move slower
A “band” is a
collection of DNA
fragments of one
particular length
Power
source
Shorter
fragments
move faster
DNA attracted to +
pole due to PO4– groups

36. Applications of DNA profiling
Forensics - to show guilt or innocence
Establishing paternity
Identification of human remains
Species identification
Evidence for sale of products from endangered species
The stability of DNA provides substantial advantages in DNA profiling, as the following example shows. In San Diego, California, there was a case of an 8-year old girl who was abducted from her home and sexually abused. Police accused the girl’s father even though she claimed that a stranger had assaulted her. The father was arrested when the child changed her story, two years after the incident. As evidence was gathered to prepare for the father’s defense, a reexamination of the child’s nightgown revealed semen stains. The DNA pattern excluded the father and included a suspect who had been jailed on child molestation charges six weeks after the girl’s assault.
For Discovery Video DNA Forensics, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Television programs might lead some students to expect DNA profiling to be quick and easy. Ask students to consider why DNA profiling actually takes many days or weeks to complete.
2. Students might expect DNA profiling for criminal investigations to involve an analysis of the entire human genome. Consider explaining why such an analysis is unrealistic and unnecessary. Modules 12.12–12.16 describe methods used to describe specific portions of the genome of particular interest.
Teaching Tips
1. Although the statistical odds of a DNA-profiling match can exceed one in 10 billion, the odds of a mistake in the collecting and testing procedures can be much greater. This is an important distinction. An error as simple as mislabeling a sample can confuse the results. Unfortunately, the odds of human error will vary and are difficult to determine.

37. 2. Recombinant DNA technology/ Genetically Modified organisms
Recombinant DNA is formed by joining DNA sequences from two different sources: .
Bacterial Plasmids (small, circular DNA molecules independent of the bacterial chromosome) are often used as vectors
Student Misconceptions and Concerns
1. Student comprehension of restriction enzymes, nucleic acid probes, and many other aspects of recombinant DNA techniques depends upon a comfortable understanding of basic molecular genetics. Consider addressing Chapter 12 after an exam that covers the content in Chapters 10 and 11.
2. Students might bring some awareness and/or concerns about biotechnology to the classroom, for example, in their reactions to the controversies regarding genetically modified (GM) foods. This experience can be used to generate class interest and to highlight the importance of good information when making judgments. Consider starting class with a headline addressing one of these issues.
Teaching Tips
1. Figure 12.1 is a synthesis of the techniques discussed in further detail in Modules 12.2–12.5. Figure 12.1 is therefore an important integrative piece that lays the foundation of most of the biotechnology discussion. Referring to this figure in class helps students relate the text to your lecture.
2. The general genetic engineering challenge discussed in Module 12.1 begins with the need to insert a gene of choice into a plasmid. This process is very similar to film or video editing. What do we need to do to insert a minute of one film into another? We will need techniques to cut and remove the minute of film and a way to cut the new film apart and insert the new minute. In general, this is also like removing one boxcar from one train, and transferring the boxcar to another train. Students can become confused by the details of gene cloning through misunderstanding this basic relationship.

38. Recombinant cells and organisms can mass-produce gene products
Common prokaryotic host: E. coli bacterium
Has many advantages in gene transfer, cell growth, and quantity of protein production
Common eukaryotic hosts:
Yeast: S. cerevisiae
“Pharm” animals
Will secrete gene product in milk
Student Misconceptions and Concerns
1. The genetic engineering of organisms can be controversial, creating various degrees of social unease and resistance. Yet, many debates about scientific issues are confused by misinformation. This provides an opportunity for you to assign students to take a position on such issues and support their arguments with accurate research. Students might debate whether a food or drug made from GM/transgenic organisms should be labeled as such, or discuss the risks and advantages of producing GM organisms.
2. The fact that the technologies described in this chapter can be used to swap genes between prokaryotes and eukaryotes reveals the fundamental similarities in genetic mechanisms shared by all forms of life. This very strong evidence of common descent provides proof of evolution that may be missed by your students.
Teaching Tips
1. As noted in Module 12.6, DNA technology is primarily used to produce proteins. Challenge your students to explain why lipids and carbohydrates are not typically produced by these processes.

39. Table 12.6 Some Protein Products of Recombinant DNA Technology.

40. Advantages of recombinant DNA products
Advantages of recombinant DNA products
Advantages of recombinant DNA products:
Identity to human protein: Recombinant DNA products of human genes have the same amino acid sequence as natural human proteins, thus avoiding allergic reactions from using proteins of other species. For example, cow insulin, with three amino acid differences from human insulin, was shown to be more allergenic than pig insulin, with one difference.
Purity: Recombinant DNA products are free of contaminants, leading to fewer side effects. For example, vaccinations can occur with a single protein from the invader’s surface rather than a heterogeneous mixture of components arising from growing and inactivating the invader prior to injection.
Quantity: Recombinant DNA products can be manufactured in large amounts. This has allowed treatments with proteins that are normally produced only in small quantities in the body. For example, interferons are natural proteins produced by white blood cells that stimulate responses to infectious agents and tumor cells. Clinical testing of interferons for cancer treatment was only possible with recombinant DNA methods that allowed the production of therapeutic amounts of these proteins.
Student Misconceptions and Concerns
1. The genetic engineering of organisms can be controversial, creating various degrees of social unease and resistance. Yet, many debates about scientific issues are confused by misinformation. This provides an opportunity for you to assign students to take a position on such issues and support their arguments with accurate research. Students might debate whether a food or drug made from GM/transgenic organisms should be labeled as such, or discuss the risks and advantages of producing GM organisms.
2. The fact that the technologies described in this chapter can be used to swap genes between prokaryotes and eukaryotes reveals the fundamental similarities in genetic mechanisms shared by all forms of life. This very strong evidence of common descent provides proof of evolution that may be missed by your students.
Teaching Tips
1. Annual flu vaccinations are a common way to prevent diseases that cannot be easily treated. However, students might not understand why many people receive the vaccine every year. A new annual vaccine is necessary because the flu viruses keep evolving, another lesson in evolution that may be missed by your students.

41. Genetically modified (GM)
Genetically modified (GM)
Transgenic organisms contain at least one gene from another species
GM plants:
Resistance to herbicides: Roundup Ready Soybeans contain a bacterial version of an amino acid synthesis enzyme that is less sensitive to glyphosate (Roundup).
Resistance to pests: Bt corn produces an insect toxin, derived from the bacterium Bacillus thuringiensis.
Improved nutritional profile: “Golden rice” has increased beta-carotene due to the presence of daffodil genes.
GM animals:
Improved qualities: Sheep with an extra copy of a growth hormone gene grow larger and faster and produce more milk and wool.
Production of proteins or therapeutics: “Pharm” animals (see Module 12.6).
The first GM organism approved for sale as food was the Flavr-Savr tomato. The modification was intended to prolong the shelf life of the tomato by keeping it from softening when ripe. Softening is caused by an enzyme called polygalacturonase that breaks down pectins in fruit. In the Flavr-Savr tomato, production of polygalacturonase was blocked by an antisense RNA molecule complementary to the enzyme’s mRNA. The shelf life of the tomato was indeed prolonged, but ultimately there was little flavor to savor as consumers found the fruit to have a bland taste!
For Discovery Video Transgenics, go to Animation and Video Files.
Student Misconceptions and Concerns
1. The genetic engineering of organisms can be controversial, creating various degrees of social unease and resistance. Yet, many debates about scientific issues are confused by misinformation. This provides an opportunity for you to assign students to take a position on such issues and support their arguments with accurate research. Students might debate whether a food or drug made from GM/transgenic organisms should be labeled as such, or discuss the risks and advantages of producing GM organisms.
2. The fact that the technologies described in this chapter can be used to swap genes between prokaryotes and eukaryotes reveals the fundamental similarities in genetic mechanisms shared by all forms of life. This very strong evidence of common descent provides proof of evolution that may be missed by your students.
Teaching Tips
1. Roundup Ready Corn, a product of the agricultural biotechnology corporation Monsanto, is resistant to the herbicide Roundup. The general strategy for farmers is to spray fields of Roundup Ready corn with the herbicide Roundup, killing weeds but not the corn. A search of the Internet will quickly reveal the controversy associated with this and other genetically modified organisms (GMO), which can encourage interesting discussions and promote critical thinking skills. Module 12.9 discusses some of the issues related to the concerns over the use of GM organisms.

42. Agrobacterium tumefaciens
DNA containing
gene for desired trait
Plant cell 1 2 3 Ti
plasmid
Recombinant
Ti plasmid
Insertion of gene
into plasmid
Introduction
into plant
cells
Regeneration
of plant
Figure 12.8A Using the Ti plasmid as a vector for genetically engineering plants.
A modified form of the Ti (tumor inducing) plasmid is used in plant genetic engineering. The tumor inducing genes have been removed from the plasmid but genes required for insertion into plant chromosomes have been retained. The gene of interest has been inserted into the plasmid under the control of a bacterial promoter.
DNA carrying new gene
Plant with new trait
Restriction site

43. Pros?
GM plants
GM animals

44. Cons?
Bt corn (see notes for Module 12.8) has been the focus of two ecological concerns. The first is related to the development of resistance to Bt toxin by the European corn borer. Those insects that can survive the levels of Bt toxin produced by the corn will reproduce, and the level of resistance to the toxin will increase among their offspring. Bt corn has been formulated to provide a high dose of the toxin to eliminate the majority of corn borers that come into contact with it. In addition, farmers are required to provide a “refuge,” a field planted with non-Bt corn where susceptible corn borers can survive. The rationale is that these susceptible corn borers will interbreed with resistant ones that survive the Bt toxin, and the resulting offspring with lowered resistance will be subject to the high toxin levels from Bt corn. Farmers are concerned that the cost of planting a field where corn borers damage the crop will not be offset by the gains of planting Bt corn on the remaining fields.
A second possible cause for concern is related to the spread of Bt corn pollen beyond the edges of a cornfield. A laboratory study showed 50% mortality for larvae of the monarch butterfly feeding on leaves of milkweed plants dusted with Bt corn pollen. A field study using potted milkweed plants at various distances from a Bt corn field showed 19% mortality for monarch larvae feeding on plants closest to the field. The extent to which monarch larvae encounter Bt pollen under natural conditions is not known, and studies of this phenomenon are continuing.
Student Misconceptions and Concerns
1. The genetic engineering of organisms can be controversial, creating various degrees of social unease and resistance. Yet, many debates about scientific issues are confused by misinformation. This provides an opportunity for you to assign students to take a position on such issues and support their arguments with accurate research. Students might debate whether a food or drug made from GM/transgenic organisms should be labeled as such, or discuss the risks and advantages of producing GM organisms.
2. The fact that the technologies described in this chapter can be used to swap genes between prokaryotes and eukaryotes reveals the fundamental similarities in genetic mechanisms shared by all forms of life. This very strong evidence of common descent provides proof of evolution that may be missed by your students.
Teaching Tips
1. Roundup Ready Corn, a product of the agricultural biotechnology corporation Monsanto, is resistant to the herbicide Roundup. The general strategy for farmers is to spray fields of Roundup Ready corn with the herbicide Roundup, killing weeds but not the corn. A search of the Internet will quickly reveal the controversy associated with this and other genetically modified organisms (GMO), which can encourage interesting discussions and promote critical thinking skills. Module 12.9 discusses some of the issues related to the concerns over the use of GM organisms.

45. 3. Gene therapy One possible procedure:
One possible procedure:
insert functional gene into a virus
virus delivers the gene to an affected cell
Viral DNA & gene insert into the patient’s chromosome
Return the cells to the patient for growth and division
At the present time, gene therapy methods supply a functional allele but do not replace the defective one. Most currently used vectors promote random integration of a therapeutic allele into a chromosome, so the location may be far from the defective allele. The production of the functional gene product alleviates the disease symptoms.
Student Misconceptions and Concerns
1. The genetic engineering of organisms can be controversial, creating various degrees of social unease and resistance. Yet, many debates about scientific issues are confused by misinformation. This provides an opportunity for you to assign students to take a position on such issues and support their arguments with accurate research. Students might debate whether a food or drug made from GM/transgenic organisms should be labeled as such, or discuss the risks and advantages of producing GM organisms.
2. The fact that the technologies described in this chapter can be used to swap genes between prokaryotes and eukaryotes reveals the fundamental similarities in genetic mechanisms shared by all forms of life. This very strong evidence of common descent provides proof of evolution that may be missed by your students.
Teaching Tips
1. As gene therapy technology expands, our ability to modify the genome in human embryos through in vitro fertilization permits genetic modification at the earliest stages of life. Future generations of humans, like our crops today, may include those with and without a genetically modified ancestry. The benefits and challenges of these technologies raise issues many students have never considered. Our students, and the generations soon to follow, will face the potential of directed human evolution.

46. Cloned gene (normal allele) Insert normal gene into virus1
Insert normal gene
into virus
Viral nucleic acid
Retrovirus 2
Infect bone marrow
cell with virus 3
Viral DNA inserts
into chromosome
Figure One type of gene therapy procedure.
Bone marrow
cell from patient
Bone
marrow 4
Inject cells
into patient

47. 4. Genomics Genomics = Applications:
Genomics =
Applications:
Evolutionary relationships: Genomic studies showed a 96% similarity in DNA sequences between chimpanzees and humans
Medical advancement: Functions of human disease-causing genes have been determined by comparisons to similar genes in yeast
Student Misconceptions and Concerns
1. The similarities in genotypes and phenotypes among members of a human family are expected and understood by most students. Yet many students have a difficult time extrapolating this knowledge and applying it to the phylogenetic relationships of other groups. The use of genomics to test phylogenetic relationships is an enormously powerful tool for modern systematics, and genomics provides significant support of the other types of evidence for evolution.
Teaching Tips
1. The first targets of genomics were prokaryotic pathogenic organisms. Consider asking your students in class to suggest why this was a good choice. Students may note that the genomes of these organisms are smaller than eukaryotes and that many of these organisms are of great medical significance.

48. Table Some Important Completed Genomes.
This table shows the surprising estimate of 21,000 genes for humans, only 2,000 more than predicted for the nematode Caenorhabditis elegans and 4,000 fewer than the estimate for a mustard plant. Humans may be able to make a greater number of proteins with a similar number of genes, through alternative splicing mechanisms, for example. While the precise number of different types of transcripts or proteins has not been determined for humans, estimates range from 47,000 to 100,000.

49. Human Genome Project Goals:
Goals:
To determine the nucleotide sequence all DNA in the human genome
To identify the location and sequence of every human gene
Student Misconceptions and Concerns
1. The similarities in genotypes and phenotypes among members of a human family are expected and understood by most students. Yet many students have a difficult time extrapolating this knowledge and applying it to the phylogenetic relationships of other groups. The use of genomics to test phylogenetic relationships is an enormously powerful tool for modern systematics, and genomics provides significant support of the other types of evidence for evolution.
2. Students might assume that the term junk DNA implies that these noncoding regions of DNA are useless. This might be a good time to note the old saying, absence of evidence is not evidence of absence. Our current inability to understand the role(s) of noncoding DNA does not necessarily mean that these regions have no significance.
3. Students might know that humans have 23 pairs of chromosomes. Consider asking them how many different types of chromosomes are found in humans. Some will not have realized that there are 24 types, 22 autosomes plus X and Y sex chromosomes.
Teaching Tips
1. The main U.S. Department of Energy Office website in support of the human genome project is found at
2. The website for the National Center for Biotechnology Information, noted in Module 12.18, is The center, established in 1988, serves as a national resource for biomedical information related to genomic data.
3. The authors note that there are 2.9 billion nucleotide pairs in the human genome. There are about 2.9 billion seconds in 91.9 years. This simple reference can add meaning to the significance of these large numbers.
4. Challenge students to explain why a complete understanding of an organism’s genome and proteomes is still not enough to understand the full biology of an organism. Ask them to consider the role of the environment in development and physiology. (One striking example of the influence of the environment is that the sex of some reptiles is determined not by the inheritance of certain chromosomes, but by incubation temperature.)
5. Students may enter your course with little appreciation of the scientific questions that remain unanswered. Struggling with the details of what we now know can overwhelm our students, leaving little room to wonder about what is not yet understood. The surprises and questions noted in Modules 12.18–12.21 reveal broad challenges that await the work of our next generation of scientists. Emphasize the many opportunities that exist to resolve unanswered questions, here and throughout your course, as an invitation to future work for students.

50. Results of the Human Genome Project
21,000 genes in 3.2 billion nucleotide pairs
Only 1.5% of the DNA codes for proteins
The remaining 88.5% of the DNA contains
Control regions (promoters, enhancers)
Unique noncoding DNA
Repetitive DNA
Student Misconceptions and Concerns
1. The similarities in genotypes and phenotypes among members of a human family are expected and understood by most students. Yet many students have a difficult time extrapolating this knowledge and applying it to the phylogenetic relationships of other groups. The use of genomics to test phylogenetic relationships is an enormously powerful tool for modern systematics, and genomics provides significant support of the other types of evidence for evolution.
2. Students might assume that the term junk DNA implies that these noncoding regions of DNA are useless. This might be a good time to note the old saying, absence of evidence is not evidence of absence. Our current inability to understand the role(s) of noncoding DNA does not necessarily mean that these regions have no significance.
3. Students might know that humans have 23 pairs of chromosomes. Consider asking them how many different types of chromosomes are found in humans. Some will not have realized that there are 24 types, 22 autosomes plus X and Y sex chromosomes.
Teaching Tips
1. The main U.S. Department of Energy Office website in support of the human genome project is found at
2. The website for the National Center for Biotechnology Information, noted in Module 12.18, is The center, established in 1988, serves as a national resource for biomedical information related to genomic data.
3. The authors note that there are 2.9 billion nucleotide pairs in the human genome. There are about 2.9 billion seconds in 91.9 years. This simple reference can add meaning to the significance of these large numbers.
4. Challenge students to explain why a complete understanding of an organism’s genome and proteomes is still not enough to understand the full biology of an organism. Ask them to consider the role of the environment in development and physiology. (One striking example of the influence of the environment is that the sex of some reptiles is determined not by the inheritance of certain chromosomes, but by incubation temperature.)
5. Students may enter your course with little appreciation of the scientific questions that remain unanswered. Struggling with the details of what we now know can overwhelm our students, leaving little room to wonder about what is not yet understood. The surprises and questions noted in Modules 12.18–12.21 reveal broad challenges that await the work of our next generation of scientists. Emphasize the many opportunities that exist to resolve unanswered questions, here and throughout your course, as an invitation to future work for students.

51. Exons (regions of genes coding for protein
or giving rise to rRNA or tRNA) (1.5%)
Repetitive
DNA that
includes
transposable
elements
and related
sequences
(44%)
Introns and
regulatory
sequences
(24%)
Unique
noncoding
DNA (15%)
Figure Composition of the human genome.
Repetitive
DNA
unrelated to
transposable
elements
(15%)