1. Genetics
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2. This lecture will help you understand:
What Is a Gene?
Chromosomes: Packages of Genetic Information
The Structure of DNA
DNA Replication
How Proteins Are Built
Genetic Mutations
How Radioactivity Causes Genetic Mutations
Meiosis and Genetic Diversity
Mendelian Genetics
More Wrinkles: Beyond Mendelian Genetics
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3. This lecture will help you understand:
The Human Genome
Cancer: Genes Gone Awry
Environmental Causes of Cancer
Transgenic Organisms and Cloning
DNA Technology—What Could Possibly Go Wrong?
History of Science: Discovery of the Double Helix
Technology: Gene Therapy
Science and Society: Genetic Counseling
Science and Society: DNA Forensics
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4. What Is a Gene?
A gene is a section of DNA that contains the instructions for building a protein.
An organism's genes make up its genotype.
The traits of an organism make up its phenotype.
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5. Chromosomes: Packages of Genetic Information
A chromosome consists of a long DNA molecule wrapped around small proteins called histones. Genes are sections of chromosomes.
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6. Chromosomes: Packages of Genetic Information
Most cells have two of each kind of chromosome. These cells are diploid, and their matched chromosomes are called homologous chromosomes.
Sperm and eggs contain only one of each kind of chromosome. They are haploid.
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7. Chromosomes: Packages of Genetic Information
Humans have 46 chromosomes (23 pairs).
One pair—the sex chromosomes—determines the sex of the person.
Males have one X and one Y chromosome. Females have two X chromosomes.
All the other chromosomes are autosomes.
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8. The Structure of DNA
A molecule of DNA consists of two strands and looks like a spiraling ladder. It is often called a double helix.
The "sides" of the ladder consist of alternating molecules of deoxyribose sugar and phosphate. The "rungs" are a series of paired nitrogenous bases.
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9. The Structure of DNA Four nitrogenous bases are used in DNA:
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
A binds with T, and G binds with C.
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10. DNA Replication During replication: DNA's two strands are separated.
Each strand serves as a template for building a new partner, following the base- pairing rules.
Each new DNA molecule includes one old strand and one new strand.
Each new DNA molecule is identical to the original.
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11. How Proteins Are Built RNA, or ribonucleic acid, plays a key role.
RNA differs from DNA in several ways:
Single-stranded instead of double-stranded
Uses ribose instead of deoxyribose sugar
Uses the nitrogenous base uracil (U) instead of thymine (T)
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12. How Proteins Are Built
DNA provides instructions for cells to build proteins through the processes of transcription and translation.
During transcription, DNA is used as a template for making an RNA molecule.
During translation, this RNA molecule is used to assemble a protein.
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13. How Proteins Are Built Transcription
In eukaryotes, transcription occurs in the cell nucleus.
The two strands of DNA separate, and one strand serves as a template for building the RNA transcript.
Transcription follows the usual base-pairing rules except that RNA uses uracil (U) instead of thymine (T).
RNA polymerase adds the free nucleotides to the growing RNA molecule.
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14. How Proteins Are Built
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15. How Proteins Are Built RNA processing Introns are removed.
Exons remain.
A cap and a tail are added.
The result is an mRNA molecule ready for translation.
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16. How Proteins Are Built Translation
Translation occurs at ribosomes in the cytoplasm.
Codons, sets of three nucleotides, are "read" from the mRNA.
Most codons represent a single amino acid to be added to the growing protein.
Stop codons tell the ribosome that no more amino acids should be added and that translation is complete.
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17. How Proteins Are Built
The genetic code
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18. How Proteins Are Built
A tRNA molecule has a set of three nucleotides, called an anticodon, and carries a single, specific amino acid.
A tRNA's anticodon binds to the mRNA's codon.
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19. Genetic Mutations
Occur when the sequence of nucleotides in an organism's DNA is changed
May result from errors during DNA replication or from exposure to things that damage DNA (UV light, X-rays, chemicals, etc.)
May have no effect, some effects, or huge effects
In eggs or sperm, may be passed down to offspring
Are the ultimate source of all genetic diversity and provide the raw materials for evolution
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20. Genetic Mutations
A point mutation occurs when one nucleotide is substituted for another.
A nonsense mutation creates a stop codon in the middle of a gene.
A frameshift mutation occurs when nucleotides are inserted or deleted, shifting the codons that are "read" during translation.
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21. Genetic Mutations
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22. How Radioactivity Causes Genetic Mutations
Ionizing radiation strikes electrons in the body, freeing them from the atoms they were attached to.
The free electrons may hit and damage DNA directly.
Free electrons may hit a water molecule, producing a free radical, a group of atoms that has an unpaired electron and is highly reactive. The free radical may then react with DNA and damage it.
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23. How Radioactivity Causes Genetic Mutations
Frequently dividing cells have less time to repair DNA damage before passing on mutations and so are more vulnerable to radiation damage.
Examples: cells in the bone marrow, lining of the digestive tract, testes, and developing fetus
Because cancer cells also divide frequently, radiation is sometimes used to treat tumors.
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24. Meiosis and Genetic Diversity
Meiosis is a form of cell division used to make haploid cells, such as eggs and sperm.
In meiosis, one diploid cell divides into four haploid cells.
During sexual reproduction, sperm and egg join to restore the normal diploid chromosome number.
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25. Meiosis and Genetic Diversity
At the beginning of meiosis, the diploid cell has already copied its DNA.
Meiosis takes place in two steps: meiosis I and meiosis II.
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26. Meiosis and Genetic Diversity
During prophase I of meiosis, crossing over occurs: Chromosomes exchange parts with their homologous chromosomes.
The chromosomes in the dividing cell are now different from those in the original cell.
Crossing over results in recombination, the production of new combinations of genes different from those found in the original chromosomes.
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27. Meiosis involves two divisions, meiosis I and meiosis II.
Phases of Meiosis
Meiosis involves two divisions, meiosis I and meiosis II.
By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells.

28. Meiosis I Meiosis I Interphase I Prophase I Metaphase I Anaphase I
Phases of Meiosis
Meiosis I
Meiosis I
Interphase I
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.
Prophase I
Metaphase I
Anaphase I
Telophase I and Cytokinesis

29. Phases of Meiosis
Cells undergo a round of DNA replication, forming duplicate chromosomes.
Interphase I
Interphase I - Cells undergo a round of DNA replication, forming duplicate chromosomes.

30. There are 4 chromatids in a tetrad.
Phases of Meiosis
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
There are 4 chromatids in a tetrad.
MEIOSIS I
Prophase I
MEIOSIS I Prophase I - Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

31. Crossing-over produces new combinations of alleles.
Phases of Meiosis
When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over.
Crossing-over produces new combinations of alleles.
Crossing-over occurs during meiosis. (1) Homologous chromosomes form a tetrad. (2) Chromatids cross over one another. (3) The crossed sections of the chromatids are exchanged.

32. Spindle fibers attach to the chromosomes.
Phases of Meiosis
Spindle fibers attach to the chromosomes.
MEIOSIS I
Metaphase I
MEIOSIS I Metaphase I - Spindle fibers attach to the chromosomes.

33. Phases of Meiosis
MEIOSIS I
Anaphase I
The fibers pull the homologous chromosomes toward opposite ends of the cell.
MEIOSIS I Anaphase I - The fibers pull the homologous chromosomes toward opposite ends of the cell.

34. Nuclear membranes form. The cell separates into two cells.
Phases of Meiosis
MEIOSIS I
Telophase I and
Cytokinesis
Nuclear membranes form.
The cell separates into two cells.
The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I.
MEIOSIS I Telophase I and Cytokinesis - Nuclear membranes form. The cell separates into two cells.

35. Phases of Meiosis
Meiosis II
The two cells produced by meiosis I now enter a second meiotic division.
Unlike meiosis I, neither cell goes through chromosome replication.
Each of the cell’s chromosomes has 2 chromatids.

36. Meiosis II Phases of Meiosis Meiosis II Telophase I and Cytokinesis I
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.
Meiosis II
Telophase I and Cytokinesis I
Metaphase II
Anaphase II
Telophase II and Cytokinesis
Prophase II

37. Phases of Meiosis
MEIOSIS II
Prophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.
MEIOSIS II Prophase II - Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.

38. The chromosomes line up in the center of cell.
Phases of Meiosis
MEIOSIS II
Metaphase II
The chromosomes line up in the center of cell.
MEIOSIS II Metaphase II - The chromosomes line up in a similar way to the metaphase state of mitosis.

39. Phases of Meiosis
MEIOSIS II
Anaphase II
The sister chromatids separate and move toward opposite ends of the cell.
MEIOSIS II Anaphase II - The sister chromatids separate and move toward opposite ends of the cell.

40. Meiosis II results in four haploid (N) daughter cells.
Phases of Meiosis
MEIOSIS II
Telophase II and Cytokinesis
Meiosis II results in four haploid (N) daughter cells.
MEIOSIS II Telophase II and Cytokinesis - Meiosis II results in four haploid (N) daughter cells.

41. Gamete Formation
Gamete Formation
In male animals, meiosis results in four equal-sized gametes called sperm.
Meiosis produces four genetically different haploid cells. In males, meiosis results in four equal-sized gametes called sperm.

42. Gamete Formation
In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.
Meiosis produces four genetically different haploid cells. In females, only one large egg cell results from meiosis. The other three cells, called polar bodies, usually are not involved in reproduction.

43. Comparing Mitosis and Meiosis
Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different haploid cells.

44. Comparing Mitosis and Meiosis
Cells produced by mitosis have the same number of chromosomes and alleles as the original cell.
Mitosis allows an organism to grow and replace cells.
Some organisms reproduce asexually by mitosis.

45. Comparing Mitosis and Meiosis
Cells produced by meiosis have half the number of chromosomes as the parent cell.
These cells are genetically different from the diploid cell and from each other.
Meiosis is how sexually-reproducing organisms produce gametes.

46. Meiosis and Genetic Diversity
How does meiosis result in genetic diversity?
1. Crossing over
2. Independent separation of homologous chromosomes
The genetic diversity produced during meiosis is crucial to evolution.
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47. Mendelian Genetics
Gregor Mendel's experiments breeding pea plants explained many hereditary patterns.
Mendel demonstrated the existence of dominant and recessive traits.
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48. Genes and Dominance
Genes and Dominance
A trait is a specific characteristic that varies from one individual to another.
Mendel studied seven pea plant traits, each with two contrasting characters.
He crossed plants with each of the seven contrasting characters and studied their offspring.

49. Each original pair of plants is the P (parental) generation.
Genes and Dominance
Each original pair of plants is the P (parental) generation.
The offspring are called the F1, or “first filial,” generation.
The offspring of crosses between parents with different traits are called hybrids.

50. Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s F1 Crosses on Pea Plants
When Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.

51. Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s Seven F1 Crosses on Pea Plants
Mendel’s F1 Crosses on Pea Plants
When Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.

52. Mendel's first conclusion
Genes and Dominance
Mendel's first conclusion
was that biological inheritance is determined by factors that are passed from one generation to the next.
Today, scientists call the factors that determine traits genes.

53. The different forms of a gene are called alleles.
Genes and Dominance
Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.
The different forms of a gene are called alleles.
Mendel’s second conclusion
is called the principle of dominance.

54. Genes and Dominance
The principle of dominance states that some alleles are dominant and others are recessive.

55. Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s F1 Crosses on Pea Plants
When Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.

56. Mendelian Genetics
Mendel postulated that the genes that determine traits consist of two separate alleles. One allele is inherited from each parent.
Mendel's principle of segregation: When an individual makes sex cells (sperm or eggs), half the sex cells carry one allele, and the other half carry the other allele.
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57. Mendelian Genetics
Mendel bred two pea plants that varied in a single trait --for example, round peas (RR) and wrinkled peas (rr).
The offspring inherited one R (round pea) allele and one r (wrinkled pea) allele. They were Rr.
All of the offspring expressed the dominant characteristic— they had round peas.
In the second generation, self-fertilizing the Rr plants resulted in a 3:1 ratio of round-pea plants to wrinkled-pea plants.
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58. Mendelian Genetics
Mendel's principle of independent assortment: The inheritance of one trait is independent of the inheritance of a second trait.
Mendel demonstrated this by crossing plants with two different traits.
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59. Independent Assortment
To determine if the segregation of one pair of alleles affects the segregation of another pair of alleles, Mendel performed a two-factor cross.

60. Independent Assortment
The Two-Factor Cross: F1  
Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy).
RRYY x rryy
All of the F1 offspring produced round yellow peas (RrYy).

61. Independent Assortment
The alleles for round (R) and yellow (Y) are dominant over the alleles for wrinkled (r) and green (y).
When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation.

62. Independent Assortment
The Two-Factor Cross: F2 
Mendel crossed the heterozygous F1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F2 generation.
RrYy × RrYy

63. Independent Assortment
The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F2 generation.
Represents:
Independent Assortment
When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation.

64. Independent Assortment
The alleles for seed shape segregated independently of those for seed color. This principle is known as independent assortment.
Genes that segregate independently do not influence each other's inheritance.

65. Independent Assortment
The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.
Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

66. More Wrinkles: Beyond Mendelian Genetics
In incomplete dominance, there are two alleles and neither is dominant. The heterozygote has an intermediate trait.
Example: snapdragon color
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67. Beyond Dominant and Recessive Alleles
Incomplete Dominance 
When one allele is not completely dominant over another it is called incomplete dominance.
In incomplete dominance, the heterozygous phenotype is between the two homozygous phenotypes.

68. Beyond Dominant and Recessive AllelesRR
A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW). WW
Some alleles are neither dominant nor recessive. In four o’clock plants, for example, the alleles for red and white flowers show incomplete dominance. Heterozygous (RW) plants have pink flowers—a mix of red and white coloring.