Chapter 14

1. Chapter 14 Mendel and the Gene Idea

2. Figure 14.1 • Gregor Mendel • experiments with garden peas

3. Mendel’s Experimental Approach • Why peas? = available in many varieties = could strictly control mating

4. Mendel’s Experimental Approach Stamens (Male) Carpel (Female)

5. Mendel’s Experimental Approach

6. Mendel’s Experimental Approach

8. Genetics Vocabulary Alternative versions of genes = Alleles

9. Organism inherits 2 alleles: 1 from mom, 1 from dad A genetic locus is represented twice Genetics Vocabulary

10. Genetics Vocabulary If the two alleles at a locus differ… Dominant allele = determines appearance Recessive allele = no noticeable effect on appearance

11. Genetic Vocabulary: Homozygous vs. Heterozygous Homozygous for a particular gene Identical pair of alleles for that gene Ex: PP (2 purple flower alleles) True-breeding - Homozygous dominant (PP) - Homozygous recessive (pp)

12. Homozygous vs. Heterozygous Homozygous for a particular gene Identical pair of alleles for that gene Ex: PP (2 purple flower alleles) True-breeding Heterozygous for a particular gene Has a pair of alleles that are different for that gene Ex: Pp (1 purple allele, 1 white allele)

13. Homozygous or Heterozygous?

14. Genetics Vocabulary An organism’s genotype (EX: Pp, PP, pp) genetic makeup An organism’s phenotype (Ex: Purple or white) physical appearance

15. Phenotype versus genotype

16. Phenotype versus genotype

17. Mendel used : • Characters that varied in an “either-or” manner • Varieties that were “true-breeding”

18. Typical Mendelian Experiment Parental Generation Hybridization F1 Generation F1 self-pollinate F2 generation

19. All Purple Hybrids 3:1 Purple : White

20. Does Mendel’s segregation model account for the 3:1 ratio observed in the F2 generation? • We can answer this question using a Punnett square

24. Other pea plant characters

25. Construct a Punnett Square for the following crosses: • Seed color: Y = Yellow, y = green • YY X Yy • Expected ratio observed in offspring? • Seed shape: R = Round, r = wrinkled • Rr X rr • Expected ratio observed in offspring?

26. The Testcross • In pea plants with purple flowers • Genotype is not obvious (Pp or PP)? = Perform testcross

27. The testcross

28. The testcross

29. Monohybrid Cross Mendel Followed a single trait (ex: flower color) • The P = true-breeding (PP or pp) • The F1 offspring = monohybrids (heterozygous for one character) (Pp)

30. Dihybrid Cross • Mendel followed 2 characters at the same time • P generation = Cross two, true-breeding parents differing in two characters • YYRR X yyrr

31. Character 1 Y =YELLOW y =green Character 2 R=ROUND r = wrinkled

32. Mendel followed 2 characters at the same time • P generation = Cross two, true-breeding parents differing in two characters • YYRR X yyrr • F1 generation = Produces dihybrids (heterozygous for both characters) • YyRr

34. 2. Independent Assortment of Chromosomes

35. 2. Independent Assortment of Chromosomes Homologous orient randomly at metaphase I of meiosis

36. How are two characters transmitted from parents to offspring? 1. As a package? (Ex: yellow and round YR) • =Dependent Assortment 2. Independently? • =Independent Assortment

37. A dihybrid cross YR Yr yR yr ? Only YR and yr as inherited from P generation? Make a punnett square for each case

39. Concept 14.2: The rules of probability govern Mendelian inheritance • Multiplication Rule • Addition Rule

40. The Multiplication and Addition Rules Applied to Monohybrid Crosses • The multiplication rule • Probability that two or more independent events will occur together • Ex: coin toss • Heads ½ X Heads ½ = ¼

41. Ex: Probability in a monohybrid cross

42. Rule of Addition • Probability that any one of two or more exclusive events will occur Ex: Heterozygotes: ¼Rr + ¼rR = ½

43. A multi-character cross = two or more independent monohybrid crosses occurring simultaneously • Calculate the chances for various genotypes: 1. Consider each character separately 2. Go back to question being asked 3. Multiply individual probabilities together 4. Use Rule of addition (if necessary)

44. 3 characters = trihybrid cross • Purple flowers (Pp), Yellow (Yy), Round (Rr) • Purple flowers (Pp), green (yy), wrinkled (rr) • PpYyRr X Ppyyrr Question: What percentage of the offspring from this cross would be predicted to have purple flowers and green and wrinkled seeds?

45. 1. Consider each character separately (make a punnett square for each character) PpYyRr X Ppyyrr: • Pp X Pp = • Yy X yy = • Rr X rr =

46. 1. Consider each character separately (make a punnett square for each character) • PpYyRr X Ppyyrr • Pp X Pp = ¼ PP, ½ pP, ¼ pp • Yy X yy = ½ Yy, ½ yy • Rr X rr = ½ Rr, ½ rr

47. 2. Go back to the original Question PpYyRr X Ppyyrr • Pp X Pp = ¼ PP, ½ pP, ¼ pp • Yy X yy = ½ Yy, ½ yy • Rr X rr = ½ Rr, ½ rr Question: What percentage of the offspring from this cross would be predicted to have purple flowers and green and wrinkled seeds? Start by listing all genotypes that fulfill this condition:

48. 2. Go back to the original Question PpYyRr X Ppyyrr • Pp X Pp = ¼ PP, ½ Pp, ¼ pp • Yy X yy = ½ Yy, ½ yy • Rr X rr = ½ Rr, ½ rr Question: What percentage of the offspring from this cross would be predicted to have purple flowers and green and wrinkled seeds? Start by listing all genotypes that fulfill this condition: Ppyyrr, PPyyrr

49. 3. Calculate probability for each genotype • Pp X Pp = ¼ PP, ½ pP, ¼ pp • Yy X yy = ½ Yy, ½ yy • Rr X rr = ½ Rr, ½ rr • Ppyyrr ½ X ½ X ½ = 2/16 • Ppyyrr

50. 3. Calculate probability for each genotype • Pp X Pp = ¼ PP, ½ pP, ¼ pp • Yy X yy = ½ Yy, ½ yy • Rr X rr = ½ Rr, ½ rr • Ppyyrr ½ X ½ X ½ = 2/16 • PPyyrr ¼ X ½ X ½ =1/16