Introduction to Genetics (Chap 11)

1. Introduction to Genetics (Chap 11) Do any two zebras have the same stripe pattern? The Study of Heredity 1

2. A Quick Review • Do you look like your parents ? Why? Because they gave you your DNA. • How is this information transferred? Through sex • What do we call a segment of DNA that codes for a protein? Gene • Where are the genes located? On the chromosomes • How many chromosomes do humans have? 46 • How many genes are on each chromosome? Depends but it is estimated about 30,000 genes in a human genome. 2

3. Introductory Terms • Genetics is the study of heredity • Gene - a segment of DNA that codes for a protein. • Allele - different forms or physical expressions of a gene. • Example: Your thumb has 2 alleles: bent and straight. 3

4. Introductory Terms cont. • Trait - a specific characteristic that varies from one individual to another • Hybrid - The offspring of crosses between parents with different traits. 4

5. Gregor Mendel • “Father of Genetics”. • Austrian monk studied math & science. • Studied variation of traits in pea plants. • Showed that the inheritance of traits follows certain laws. 5

6. The Work of Gregor Mendel 6

7. Mendel’s Experiment • Cross-bred pea plants with different traits. • Studied 7 plant traits (seed/pea shape, color, height, etc.) of the hybridoffspring Mendel’s Seven F1 Crosses on Pea Plants Seed Shape Seed Color Pod Color Flower Position Plant Height Seed Coat Color Pod Shape Smooth Green Axial Tall Round Yellow Gray Wrinkled Green White Constricted Yellow Terminal Short 7 Round Yellow Gray Smooth Green Axial Tall

8. F1 Generation • The 1st generation (F1) had the characteristics of onlyone of the parent plants (P) • Why did the “short” trait appear in the F2 generation but not in the F1 generation? P Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short 8

9. F1 Generation • The 2nd generation (F2) had characteristics of BOTH parent plants (P). Always 3:1 ratio. • Why did the “short” trait appear in the F2 generation but not in the F1 generation? P Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short 9

10. Segregation (to separate). • During gamete (sex cell) formation, alleles separate. Each gamete carries only a single copy of each gene. • What are the two types of Gametes (sex cells)? 10

11. Segregation (to separate) • Each F1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness. 11

12. Mendel’s Conclusions. • Principal of Unit characters -Every trait such as height, color, etc. are inherited separately * Not necessarily true! 12

13. B. Principal of Dominance • Some unit characters (alleles) mask others when they are present these are called dominant alleles. • Represented by capitol letters of the dominant trait. • The recessive allele is represented by the same letter but in lower case. 13

14. B. Principal of Dominance • In garden peas tall is dominant over short (TT, Tt, tt). 14

15. Principal of Segregation- In the formation of sex cells (gametes), one member of each allele separates into different sex cells. 15

16. Principal of Independent Assortment- Genes for different traits can separate independently during the formation of gametes. * Also, not necessarily true! 16

17. Quiz! • Gametes are also known as • genes. • sex cells. • alleles. • hybrids. 17

18. Quiz! • The offspring of crosses between parents with different traits are called • alleles. • hybrids. • gametes. • dominant. 18

19. Quiz! • In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F1 generation consists of • all short plants. • all tall plants. • half tall plants and half short plants. • all plants of intermediate height. 19

20. Probability & Punnett Square • How do geneticists use the principles of probability? • The principles of probability can be used to predict the outcomes of genetic crosses. 20

21. How do geneticists use Punnett squares? • Punnett squares can be used to predict and compare the genetic variations that will result from a cross. 21

22. Punnett Squares 22

23. Punnett Squares • Punnett squares can be used to predict and compare the genetic variations that will result from a cross. F1 Parents 23

24. A capital letter = dominant allele (T=tall). • A lowercase letter = recessive allele (t=short). 24

25. Gametes from each parent are on the top and left side. 25

26. Possible gene combinations (genotypes) are in the four boxes. 26

27. Genetic Terms • Genotype - genetic makeup (represented by letters) describes the two alleles of a gene. What are the genotypes? 27

28. Phenotype – What it looks like (physical traits). • What are the phenotypes? 28

29. Homozygous – both alleles are the same (purebred). • Homozygous dominate – genotype has two dominate alleles. • Homozygous recessing – genotype has two recessive alleles. • What is the homozygous dominant genotype? • What is the homozygous recessive genotype? 29

30. Heterozygous – genotype (hybrid) means one dominant and one recessive allele. • What is the heterozygous genotype? 30

31. The plants have different genotypes (TT and Tt), but they have the same phenotype (tall). 31

32. Probability & Segregation • 1/4 of the F2plants have two alleles for tallness (TT). • 1/2 have one allele for tall (T), and one for short (t). • 1/4 of the F2 have two alleles for short (tt). 32

33. Probability can be used to predict • average outcome of many events. • precise outcome of any event. • how many offspring a cross will produce. • which organisms will mate with each other. 33

34. Compared to 4 flips of a coin, 400 flips of the coin is • more likely to produce about 50% heads and 50% tails. • less likely to produce about 50% heads and 50% tails. • guaranteed to produce exactly 50% heads and 50% tails. • equally likely to produce about 50% heads and 50% tails. 34

35. Organisms that have two different alleles for a particular trait are said to be • hybrid. • heterozygous. • homozygous. • recessive. 35

36. Two F1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall? • 100% • 50% • 0% • 25% 36

37. The Punnett square allows you to predict • only the phenotypes of the offspring from a cross. • only the genotypes of the offspring from a cross. • both the genotypes and the phenotypes from a cross. • neither the genotypes nor the phenotypes from a cross. 37

38. Other Mendelian Topics • Independent Assortment • Two-Factor Cross: True-breeding pea plants with two different genes were bred: round yellow peas (RRYY) Xwrinkledgreen peas (rryy). 38

39. All F1 offspring were heterozygous for round yellow seeds. Wrinkled-green Fig 11-9 Round-Yellow 39

40. Heterozygous F1 plants (RrYy)were crossed to see if alleles would separate independently in the F2 generation. 3a The ratio 9:3:3:1 is what is expected for traits inherited independently 40

41. In Mendel’s experiment, the F2 generation produced the following: • some seeds that were round and yellow • some seeds that were wrinkled and green • some seeds that were round and green • some seeds that were wrinkled and yellow 41

42. Mendel’s conclusion: • Principal of Independent Assortment-- Genes for different traits separate independently (in gametes) & create genetic differences in plants & animals. • *This rule is broken if the two genes being crossed are close to each other on the same chromosome 42

43. In a cross involving two pea plant traits, observation of a 9 : 3 : 3 : 1 ratio in the F2 generation is evidence for: • the two traits being inherited together. • an outcome that depends on the sex of the parent plants. • the two traits being inherited independently of each other. • multiple genes being responsible for each trait. 43

44. Beyond Dominant & Recessive Alleles • Incomplete Dominance – When one allele is not completely dominant over another. • The heterozygous phenotype is between the two homozygous phenotypes.

45. Incomplete Dominance RR • A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW). WW

46. Codominance – Both alleles are equally dominant and expressed separately at 50:50 ratio. Co-dominance Rhododendron

47. Multiple alleles - Genes that are controlled by more than two alleles • In some populations more that two alleles can exist that control a trait (e.g. coat color in rabbits).

48. KEY C = full color; dominant to all other alleles cch= chinchilla; partial defect in pigmentation; dominant to ch and c alleles ch = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles • Different combinations of alleles result in the colors shown here. Full color: CC, Ccch, Cch, or Cc Chinchilla: cchch, cchcch, or cchc Himalayan: chc, or chch AIbino: cc

49. Polygenic Trait - Traits controlled by two or more genes • Skin color in humans is a polygenic trait controlled by more than four different genes.

50. 11–3 • Traits controlled by two or more genes are called • multiple-allele traits. • polygenic traits. • codominant traits. • hybrid traits.