GENETICS

1. GENETICS Unit 7

2. allele

3. How we inherit our genes Each human offspring inherits one maternal set of 23 chromosomes and one paternal set.

4. Unlucky catch A baby inheriting two copies of the defective FMO3 gene will develop fish odor syndrome.

5. Homozygous vs. Heterozygous

7. Homozygous vs. Heterozygous

8. Family resemblance: your mother and father each contribute to your genetic makeup.

9. TAKE-HOME MESSAGE • Offspring resemble their parents because they inherit genes—instruction sets for biochemical, physical, and behavioral traits, some of which are responsible for diseases—from their parents. Challenge Question • How many alleles of each gene do you have? Where did you get them?

10. heredity the passing on of physical or mental characteristics genetically from one generation to another

11. HEREDITY I AM the family face; Flesh perishes, I live on, Projecting trait and trace Through time to times anon, And leaping from place to place Over oblivion. The ears-heired feature that can In curve and voice and eye Despise the human span Of durance—that is I; The eternal think in man, That heeds no call to die. —Thomas Hardy, Moments of Vision and Miscellaneous Verses, 1917

13. HISTORY

14. History of Genetics Timeline

15. Some traits are controlled by a single gene

17. TAKE-HOME MESSAGE • Many human traits are determined by the instructions a person carries on a single gene, and the traits exhibit straightforward patterns of inheritance.

19. Another idea offspring reflect a simple blending of their two parents’ traits via the blood

20. Charles Darwin pangenesis

21. Lamarck Inheritance of Acquired Characteristics

22. Gregor Mendel: Mini-Biography

23. Mendel didn’t do anything radically new, but simply applied methodical experimentation and scientific thinking

24. Mendel chose a good organism to study: the garden pea. • relatively easy to fertilize manually by “pollen dusting” • easy to collect dozens or even hundreds of offspring from a single cross • pea plants are fast enough breeders that Mendel could conduct experiments that lasted for multiple generations

25. Mendel chose to focus on seven easily categorized traits • flower color is purple or white • seed color is yellow or green • flower position is axial or terminal • pod shape is inflated or constricted • stem length is long or short • pod color is yellow or green • seed shape is round or wrinkled

26. Mendel began his studies by first repeatedly breeding together similar plants until he had many distinct populations, each of which was unvarying for a particular trait

28. TAKE-HOME MESSAGE • In the mid-1800s, Gregor Mendel conducted studies that helped us understand how traits are inherited. • He applied methodical experimentation and rigorous hypothesis testing, focusing on easily observed and categorized traits in garden peas. Challenge Question • Why was the pea plant a good organism with which to study heredity?

29. Punnett Squares

30. Mendel’s conclusions: • that the inheritance of each trait is determined by "units" or "factors" that are passed on to descendants unchanged (these units are now called genes) • that an individual inherits one such unit from each parent for each trait • that a trait may not show up in an individual but can still be passed on to the next generation

31. Mendel's observations from these experiments can be summarized in two principles: • the principle of segregation • the principle of independent assortment

32. Principle (Law) of Segregation: • for any particular trait, the pair of alleles of each parent separate • only one allele passes from each parent on to an offspring • which allele in a parent's pair of alleles is inherited is a matter of chance • segregation of alleles occurs during the process of sex cell formation (meiosis)

34. Principle (Law) of Independent Assortment: • different pairs of alleles are passed to offspring independently of each other • result - new combinations of genes present in neither parent are possible • today, we know this is because the genes for independently assorted traits are located on different chromosomes

35. But wait…there’s more!

36. Phenotype vs. Genotype

37. Phenotype set of observable characteristics of an individual resulting from the interaction of its genotype with the environment

38. Genotype genetic constitution (“formula”) of an individual organism

40. Chance is important in genetics for two reasons: • consequence of segregation • fertilization is a chance event

43. Test Cross

44. Test cross • In this test-cross, a homozygous white female alligator is bred with a normally colored male of unknown genotype. • The color of their offspring will help identify whether the male is homozygous dominant or heterozygous.

45. Test Cross You mate a pigmented male alligator to a female albino alligator. The clutch of baby alligators includes both pigmented and albino individuals. What is the genotype of the father? • MM • Mm • mm • 1 and 2 are equally possible.

46. Take-Home Message • In a test-cross, an individual with a dominant phenotype and an unknown genotype is mated with a homozygous recessive individual. • The phenotypes of the offspring reveal the unknown genotype.

48. Pedigrees • In cross-pollinating plants that either produce yellow or green pea seeds exclusively, Mendel found that the first offspring generation (f1) always has yellow seeds.   However, the following generation (f2) consistently has a 3:1 ratio of yellow to green.

49. Pedigrees • This 3:1 ratio occurs in later generations as well.   Mendel realized that this was the key to understanding the basic mechanisms of inheritance.

50. What is the genotype of the paternal grandmother? Homozygous recessive Heterozygous Homozygous dominant Cannot be determined