1. David Sadava H. Craig Heller Gordon H. Orians William K. Purves David M. Hillis Biologia.blu B – Le basi molecolari della vita e dell’evoluzione Genetics: Mendel and Beyond

2. What are the mendelian laws of inheritance? How do alleles interact? How do genes interact? What is the relationship between genes and chromosomes? Genetics: Mendel and Beyond

3. Gregor Mendel and his garden

4. Character: observable physical feature (e.g., flower colour). Trait: form of a character (e.g., purple flowers or white flowers). A heritable trait is passed from parent to offspring. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

5. Mendel looked for well-defined, true- breeding traits—the observed trait is the only one present for many generations. True-breeding strains were isolated by inbreeding and selection. He concentrated on seven traits. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

7. Mendel’s crosses: pollen from one parent was transferred to the stigma of the other parent parental generation = P; resulting offspring = first filial generation or F 1 ; if F 1 plants self pollinate, produce second filial generation or F 2. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

8. A controlled cross between two plants

9. Mendel’s first experiment: 1.crossed plants differing in just one trait (P); 2.F 1 generation are monohybrids; 3.the monohybrids were then allowed to self pollinate to form the F 2 generation - a monohybrid cross; 4.Mendel repeated this for all seven traits. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

10. One trait of each pair disappeared in the F 1 generation and reappeared in the F 2 —these traits are recessive. The trait that appears in the F 1 is the dominant trait. The ratio of dominant to recessive in the F 2 was about 3:1. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

13. Mendel also concluded that each gamete contains only one particle (or unit), but the zygote contains two— because it is produced from the fusion of two gametes. The “particles” are now called genes. The totality of all genes in an organism is the genome. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

14. Alleles: different forms of a gene. True-breeding individuals have two copies of the same allele: they are homozygous for the allele (e.g., ss). Heterozygous individuals have two different alleles (e.g., Ss). Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

15. Phenotype: physical appearance of an organism (e.g., spherical seeds). Genotype: the genetic makeup (e.g., Ss). Spherical seeds can be the result of two different genotypes—SS or Ss. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

16. Mendel’s first and second law The Law of Dominance: in a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. The Law of Segregation: the two copies of a gene separate when an individual makes gametes. When the F 1 self-pollinates, there are three ways to get the dominant trait, only one way to get the recessive—resulting in the 3:1 ratio. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

17. Mendel’s explanation of inheritance

18. A gene is a sequence on a DNA molecule that resides at a particular site on a chromosome—the locus—and encodes a particular character. Genes are expressed as proteins with particular functions. Different alleles of a gene separate during meiosis. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

19. Meiosis accounts for the segregation of alleles (part 1)

20. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance? Meiosis accounts for the segregation of alleles (part 2)

21. Mendel tested his hypothesis by doing test crosses: he determined whether an individual is homozygous or heterozygous for a trait by crossing it with the homozygous recessive; Mendel crossed the F 1 with known homozygote’s (e.g., wrinkled or ss). Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

22. Mendel’s third law The Law of Independent Assortment Alleles of different genes assort independently during gamete formation. It doesn’t always apply to genes on the same chromosome; but chromosomes do segregate independently. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

24. Independent assortment

25. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance? Meiosis accounts for independent assortment of alleles

26. Human pedigrees can show Mendel’s laws. Humans have few offspring; pedigrees do not show the clear proportions that the pea plants showed. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance?

27. Pedigree analysis and inheritance (part 1)

28. Genetics: Mendel and Beyond - What are the mendelian laws of inheritance? Pedigree analysis and inheritance (part 2)

29. Different alleles arise through mutation: rare, stable, inherited changes in the genetic material. Wild type: allele present in most of the population; other alleles are mutant alleles. Locus with wild-type allele present less than 99% of the time is polymorphic. Genetics: Mendel and Beyond - How do alleles interact?

30. Inheritance of coat color in rabbits

31. Genetics: Mendel and Beyond - How do alleles interact? Incomplete dominance follows Mendel’s laws

32. Genetics: Mendel and Beyond - How do alleles interact? AB0 blood reactions are important in transfusions

33. Genetics: Mendel and Beyond - How do genes interact? Genes may interact epistatically

34. Genetics: Mendel and Beyond - What is the relationship between genes and chromosomes?

35. Crossing over results in genetic recombination

36. Genetics: Mendel and Beyond - What is the relationship between genes and chromosomes? Recombinant frequencies

37. Mammals: female has two X chromosomes, male has one X and one Y. Genetics: Mendel and Beyond - What is the relationship between genes and chromosomes? Birds: female has one Z and one W, male has two Z chromosomes.

38. Genetics: Mendel and Beyond - What is the relationship between genes and chromosomes? Eye colour is a sex-linked trait in Drosophila (part 1)

39. Genetics: Mendel and Beyond - What is the relationship between genes and chromosomes? Eye colour is a sex-linked trait in Drosophila (part 2)

40. Genetics: Mendel and Beyond - What is the relationship between genes and chromosomes? Red-green colour blindness is a sex-linked trait