Chapter 11 -- Basic Genetics

1. Chapter 11 -- Basic Genetics

2. Inheritance

3. Gregor Mendel 1822-1884

4. Mendel’s pea garden in Brno

5. Mendel’s paper Verhandlungen des naturforschenden Vereines in Brünn. Brünn: Vereines, 1865.

6. Why did Mendel choose peas?

7. Mendel’s Peas

8. Two Characters Seed Coat Flower color

9. Two traits per character Rough Smooth

10. Two traits per character Purple flowers White flowers

11. Traits are alternative forms of characters white or purple smooth or rough

12. “Brother Mendel! We grow tired of peas!”

14. Controlling the mating

15. No question as to parentage of offspring

16. Compare

17. 1. Start with true breeding plants. 2. Cross alternative forms among these true-breeders. Mendel’s experimental design

18. P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation

20. 3. Allowed progeny (F1) to self-fertilize and examined offspring 4. Count the number of offspring of each type Mendel’s experimental design

21. P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation

22. Monohybrid crosses: examining one trait at a time What Mendel found-monohybrid crosses

23. P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation Monohybrid Cross

24. P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers What Mendel found F1 generation

25. P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation F1 x F1

26. F1 x F1 F2: purple and white 705 purple flowered plants 224 white flowered plants 3:1 ratio What Mendel found F2 generation

27. F1 Generation (hybrids) All plants had purple flowers F2 Generation 224 white 705 purple 3:1 ratio

28. Mendel’s 7 pea traits

29. 1. Alternative versions of genes lead to variations in inherited characters. Alternative versions are called alleles 2. Each individual receives 2 alleles. homozygotes: 2 copies of identical allele heterozygotes: two different alleles Mendel’s model

30. 3. In heterozygotes only the dominant form of allele will be expressed. genotype: alleles present phenotype: physical appearance 4. Alleles segregate from one another into gametes (Law of segregation) Mendel’s model

31. Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers Chromosomes, genes and alleles ……..

32. Genes control characters e.g., flower color

33. Genes control characters Traits are alternative forms of characters e.g., white or purple

34. Genes control characters Traits are alternative forms of characters Alleles are alternative forms of a gene

36. Human Chromosomes

37. Genes and Alleles

38. Variationwithin a population

39. Capital letter for dominant allele; lower case letter for recessive allele Example flower color: P = dominant allele p = recessive allele Mendel used symbols to interpret results

40. Phenotype: purple Genotype: PP or Pp

41. Phenotype: white Genotype: pp

42. Genotype Phenotype PP (homozygous Purple 1 Pp (heterozygous 3 Purple 2 Pp (heterozygous Purple pp (homozygous White 1 1 Ratio 1:2:1 Ratio 3:1

43. Cross plant with unknown genotype with homozygous recessive The testcross

44. The Punnett square Reginald C. Punnett

46. PP x pp p p P Pp Pp Pp Pp P

47. Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp If Pp, then 1 2 offspring purple and 1 2 offspring white: If PP, then all offspring purple: p p p p P P Pp Pp Pp Pp P P pp pp Pp Pp The testcross

48. Different types of Inheritance

49. Dominant - Recessive

50. Pp PP pp white purple