Chromosomes and Human Inheritance

1. Chromosomes and Human Inheritance Chapter 12

2. Impacts, Issues:Strange Genes, Tortured Minds • Exceptional creativity often accompanies neurobiological disorders such as schizophrenia, autism, chronic depression, and bipolar disorder • Examples: Lincoln, Woolf, and Picasso

3. 12.1 Human Chromosomes • In humans, two sex chromosomes are the basis of sex – human males have XY sex chromosomes, females have XX • All other human chromosomes are autosomes – chromosomes that are the same in males and females

4. Sex Determination in Humans • Sex of a child is determined by the father • Eggs have an X chromosome; sperm have X or Y

5. Sex Determination in Humans • The SRY gene on the Y chromosome is the master gene for male sex determination • Triggers formation of testes, which produce the male sex hormone (testosterone) • Without testosterone, ovaries develop and produce female sex hormones (estrogens)

6. Sexual Development in Humans

7. diploid germ cells in male diploid germ cells in female meiosis, gamete formation in both female and male: eggs sperm X Y × X X × fertilization: X X X XX XX XY Y XY sex chromosome combinations possible in the new individual Fig. 12-2a, p. 186

8. Fig. 12-2bc, p. 186

9. At seven weeks, appearance of “uncommitted” duct system of embryo At seven weeks, appearance of structures that will give rise to external genitalia Y chromosome present Y chromosome absent Y chromosome present Y chromosome absent testes ovaries 10 weeks 10 weeks ovary penis vaginal opening uterus vagina penis birth approaching testis b c Fig. 12-2bc, p. 186

10. Animation: Human sex determination

11. Karyotyping • Karyotype • A micrograph of all metaphase chromosomes in a cell, arranged in pairs by size, shape, and length • Detects abnormal chromosome numbers and some structural abnormalities • Construction of a karyotype • Colchicine stops dividing cells at metaphase • Chromosomes are separated, stained, photographed, and digitally rearranged

12. Karyotyping

13. Fig. 12-3a, p. 187

14. Fig. 12-3b, p. 187

15. Animation: Karyotype preparation

16. 12.1 Key ConceptsAutosomes and Sex Chromosomes • All animals have pairs of autosomes – chromosomes that are identical in length, shape, and which genes they carry • Sexually reproducing species also have a pair of sex chromosomes; the members of this pair differ between males and females

17. 12.2 Autosomal Inheritance Patterns • Many human traits can be traced to autosomal dominant or recessive alleles that are inherited in Mendelian patterns • Some of those alleles cause genetic disorders

18. Autosomal Dominant Inheritance • A dominant autosomal allele is expressed in homozygotes and heterozygotes • Tends to appear in every generation • With one homozygous recessive and one heterozygous parent, children have a 50% chance of inheriting and displaying the trait • Examples: achondroplasia, Huntington’s disease

19. Autosomal Recessive Inheritance • Autosomal recessive alleles are expressed only in homozygotes; heterozygotes are carriers and do not have the trait • A child of two carriers has a 25% chance of expressing the trait • Example: galactosemia

20. Autosomal Inheritance

21. Fig. 12-4a, p. 188

22. Fig. 12-4b, p. 188

23. Animation: Autosomal dominant inheritance

24. Animation: Autosomal recessive inheritance

25. Galactosemia

26. Neurobiological Disorders • Most neurobiological disorders do not follow simple patterns of Mendelian inheritance • Depression, schizophrenia, bipolar disorders • Multiple genes and environmental factors contribute to NBDs

27. 12.3 Too Young to be Old • Progeria • Genetic disorder that results in accelerated aging • Caused by spontaneous mutations in autosomes

28. 12.2-12.3 Key ConceptsAutosomal Inheritance • Many genes on autosomes are expressed in Mendelian patterns of simple dominance • Some dominant or recessive alleles result in genetic disorders

29. 12.4 Examples of X-Linked Inheritance • X chromosome alleles give rise to phenotypes that reflect Mendelian patterns of inheritance • Mutated alleles on the X chromosome cause or contribute to over 300 genetic disorders

30. X-Linked Inheritance Patterns • More males than females have X-linked recessive genetic disorders • Males have only one X chromosome and can express a single recessive allele • A female heterozygote has two X chromosomes and may not show symptoms • Males transmit an X only to their daughters, not to their sons

31. X-Linked Recessive Inheritance Patterns

32. Animation: X-linked inheritance

33. Some X-Linked Recessive Disorders • Hemophilia A • Bleeding caused by lack of blood-clotting protein • Red-green color blindness • Inability to distinguish certain colors caused by altered photoreceptors in the eyes • Duchenne muscular dystrophy • Degeneration of muscles caused by lack of the structural protein dystrophin

34. Hemophilia A in Descendents of Queen Victoria of England

35. Red-Green Color Blindness

36. Fig. 12-9a, p. 191

37. Fig. 12-9b, p. 191

38. Fig. 12-9c, p. 191

39. Fig. 12-9d, p. 191

40. 12.4 Key ConceptsSex-Linked Inheritance • Some traits are affected by genes on the X chromosome • Inheritance patterns of such traits differ in males and females

41. 12.5 Heritable Changes in Chromosome Structure • On rare occasions, a chromosome’s structure changes; such changes are usually harmful or lethal, rarely neutral or beneficial • A segment of a chromosome may be duplicated, deleted, inverted, or translocated

42. Duplication • DNA sequences are repeated two or more times; may be caused by unequal crossovers in prophase I

43. normal chromosome one segment repeated p. 192

44. Deletion • Loss of some portion of a chromosome; usually causes serious or lethal disorders • Example: Cri-du-chat

45. segment C deleted p. 192

46. Deletion: Cri-du-chat

47. Fig. 12-10a, p. 192

48. Fig. 12-10b, p. 192

49. Inversion • Part of the sequence of DNA becomes oriented in the reverse direction, with no molecular loss

50. segments G, H, I become inverted p. 192