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Chromosomes and Human Inheritance

Chromosomes and Human Inheritance

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Chromosomes and Human Inheritance

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  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