1. Ch 14 Human Genetics

2. The Role of Chromosomes
Genome – the full set of genetic information that an organism carries in its DNA.
Karyotype – shows a picture of chromosomes
- Chromosomes are always in pairs.
- Arranged in order of decreasing size.
- The last pair of chromosomes, or the 23rd pair are called the sex chromosomes.
- Males (XY)
- Females (XX)
- Autosomes do not determine a
person’s gender. They are body
chromosomes. They determine ones characteristics!
- Chromosome #1-22

3. Karyotype
- Amniocentesis, a sampling of the fetal fluid which then can help determine if there are any genetic disorders of the developing fetus.
- Geneticist will look at the chromosomes of the fetus.
- Chromosomes are taken during mitosis because they are fully condensed and visible.

4. Does any of the following fit with Mendel’s Conclusions?
Cross red flower and white 4 flower??
Result: 4 pink flowers
Cross a black chicken with a white chicken??
Result: 4 black & white speckled chickens
Ending up with 4 different colored rabbits as possible offspring??
Why are there many shades of skin color and hair color in humans as opposed to just black and white?

5. Transmission of Human Traits
A. Incomplete dominance, neither allele/gene is completely dominant nor completely recessive.
- Heterozygous phenotype is in between the two homozygous phenotypes
- individual is a blend
Snap dragons (flowers)
RR= Red
WW= White
If a red snap dragon were crossed with white snapdragon, the heterozygous plant would be PINK!
RR x WW
Offspring = RW = pink

6. Codominance
- Codominant alleles/genes are both fully and separately expressed.
- Both phenotypes are shown in the Heterozygous individual.
- Black hamster crossed with a white hamster
- BB X WW
- The heterozygous
individual BW, would
be both black and white
in color. B B W BW BW BW W BW

7. Co-dominance and Multiple Alleles in Blood Types
Example: 4 Blood Types
Blood groups: 3 alleles = A (IA), B (IB), O (i)
The four blood types are Type A, Type B, Type AB, Type O

8. Blood Typing Type A Genotypes = AA (IA IA), AO (IAi)
Type B Genotypes = BB (IB IB), BO (IBi)
Type AB Genotype = AB (IA IB)
Type O Genotype = OO (ii)
A and B are always dominant to O.
AO (IAi) = A type blood
BO (IBi) = B type blood

9. A and B are NOT dominant to each other, they are Codominant
So remember… There are 3 alleles (A, B, O), however there are 4 blood types. (A, B, AB, O)

10. Punnett Square
Cross a woman Heterozygous for A-blood and a man with AB-blood
Parent genotypes:
Genotypes:
Phenotypes:
AO x AB
1IAIA :1IAIB :1IAi :1IBi IA i
1: AB type
2: A-type
1: B-type IA
IAIA
IAi IB
IAIB
IBi

11. African American Population Resistance to Malaria
More Codominance
Normal Red
Blood Cell
Sickled Red
Blood Cell
African American Population
Resistance to Malaria

12. Sickle Cell NN= Normal Blood Cells SS= Sickled Blood Cells
NS = Both Normal and Sickled Cells
Cross a heterozygous mom with a heterozygous dad for blood cells.
Parent genotypes:
Genotypes:
Phenotypes:

13. Multiple Alleles & Polygenic Traits
Genes with > 2 ALLELES
Ex) Rabbits fur color
C: wild type
Cch: chinchilla
Ch; himalyan
c: albino
Ex) Human blood types
A, B, AB, O
Polygenic Traits
Traits controlled by 2 or more GENES
Ex) hair color
Ex) eye color
Ex) skin color
More than 4 genes

14. Multiple Alleles: Rabbit Fur Color
Codominance: Erminette chickens
Multiple Alleles: Rabbit Fur Color
Incomplete Dominance:
4 o’ clock flowers

15. Genes and the Environment
Your phenotype is not just dependent on your genes, but also the environment
Examples
Sea turtles gender –determined by the temp of sand
Gender of alligators – determined by temp.
Height of people- influenced by nutrition

16. C. Sex-linked traits - Genes on the X chromosome
1. Only the X Chromosome carries genes
so if a gene is on the X chromosome, the female would have TWO of those genes
and the male would have only ONE. X Y
Female that has the disorder
Female carrier for a disorder X
Male that has the disorder

17. X & Y Chromosomes & Traits
X chromosome much larger than the Y. Has over 1,200 genes on it.
Y chromosome only has about 140 genes on it, most which are associated with male sex determination and sperm development.

18. Sex-linked traits
A genetic disorder that is found or linked to the X chromosome ONLY
Females can carry a sex-linked genetic disorder and not have the disorder.
This is known as being a carrier of the disorder.
In order for the female to have the disorder both X chromosomes must have the gene for the disorder
Males (XY) express all of their sex linked genes because they only have one X chromosome.
If the X chromosome has the gene, the male has the disorder.
Males can not be carriers because they only have one X chromosome
Examples: Hemophilia and Colorblindness

19. a sex-linked recessive trait. (C- normal vision; c- colorblindness)
In order for a female to be color blind, she would have to have two colorblind genes.
A male needs to only have one colorblind gene. X Y X

20. What do you see?

21. A woman is heterozygous for Normal vision
A woman is heterozygous for Normal vision. She marries a man who is colorblind.
What is the predicted colorblindness outcome for their children?
LET … N = normal vision and
n = color blind
Parent genotypes:
FIND THE:
Genotypic Ratio:
Phenotypic Ratio:
X N Xn Y
XN Xn x XnY
Mom Dad

22. X Chromosome Inactivation
Males and females can differ in sex linked traits.
The expression of genes on the sex chromosomes differs from the expression of autosomal genes.
Genes located on the sex chromosomes are called sex- linked genes or X-linked genes.
Males express all of the alleles on both sex chromosomes.
In females one of the two X chromosomes is randomly turned off by a process called X chromosome inactivation.

23. Human Traits
Pedigree – a chart which shows the relationships within a family.
Phenotypes are used to infer genotypes on a pedigree.
You can often determine if an allele for a trait is dominant or recessive or sex-linked.
A shaded circle or square indicates that a person expresses the trait.
A horizontal line connecting a male and a female represents a marriage.
A circle represents a female.
A square represents a male.
A vertical line and a bracket connect the parents to their children.
A circle or square that is not shaded indicates that a person does not express the trait.

24. Studying the Human Genome
1. Manipulating DNA
Because DNA is so large, in order to work with it, it must be cut into smaller pieces.
Many bacteria produce enzymes that can cut DNA
Restriction enzymes – Cut DNA into precise pieces at specific locations that are several hundred bases in length (known as restriction fragments).
When the restriction enzyme cuts the DNA, the ends are called “sticky ends” so they can bond with the complementary base sequence.

25. Studying the Human Genome
2. Separating the DNA
Gel electrophoresis – a technique used to separate and analyze the differently sized cut fragments of DNA.
The fragments of DNA are put into wells on a gel.
An electric voltage moves them down the gel.
DNA is negatively charged so they move toward the positive charge
Shorter fragments of DNA move faster than longer fragments.
Fragments appear as bands on the gel when specific stains are applied.

26. Studying the Human Genome
3. Reading DNA
The single-stranded DNA fragments are placed in a test tube containing DNA polymerase and the four nucleotide bases along with a chemical dye.
Each time a dye-labeled base is added to a new DNA strand, the synthesis of that strand stops.
The result is a series of color-coded DNA fragments of different lengths.

27. Genetic Fingerprinting
Gel Electrophoresis

28. The Human Genome Project
Launched in 1990.
A 13 year, international effort with the main goal of sequencing all 3 billion base pairs of human DNA and identifying all human genes.
Known as Shotgun sequencing
This method rapidly sorts DNS fragments by overlapping base sequences.
Locating a gene
A typical gene, such as insulin, has several DNA sequences that can serve as locators. These include the promotor, sequences between introns and exons, and start and stop codons.
Bioinformatics
A new field that combines molecular biology with information science. It is critical to studying and understanding the human genome.