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Sex Determination and Sex-linked Genes

Sex Determination and Sex-linked Genes. Genes located on X or Y chromosomes behave differently than autosomal genes. Reciprocal crosses distinguish between sex-linked and autosomal genes. 1. Sexual Differences - Human Chromosomes. 2. Sexual Differences - Drosophila Chromosomes. 3.

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Sex Determination and Sex-linked Genes

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  1. Sex Determination and Sex-linked Genes Genes located on X or Y chromosomes behave differently than autosomal genes. Reciprocal crosses distinguish between sex-linked and autosomal genes. 1

  2. Sexual Differences - Human Chromosomes 2

  3. Sexual Differences - Drosophila Chromosomes 3

  4. Sexual Determination in Drosophila Bridges - Dosage Effect X:A ratio >1.0 = female <0.5 = male Y sperm motility 4

  5. Sexual Determination in Humans Y determines maleness - SRY (sex determining region) TDF (testis determining factor) XY females - non functional TDF OR androgen insensitivity (AR defect) CAIS, PAIS 5

  6. Sexual Determination in Various Species 6

  7. Sexual Determination in Various Species 7

  8. Sexual Determination in Various Species Reptiles - Sex depends on temperature during development. Caribbean bluehead wrasse - Dominant supermale replaced by male or female Brain chemical - arginine vasotocin (AVT) 8

  9. X-linked human genes - NCBI Map Viewer 9

  10. X-linked human genes - Examples Many housekeeping (not sex related) genes Recessive X-linked traits: Color blindness, hemophilia Duschene muscular dystrophy, Lesch Nyhan syndrome, many others Dominant X-linked traits: Hypophosphatemic rickets - growth retardation, bone disease, renal defects Chondrodysplasia punctata - hydroxysteroid isomerase skin and skeletal manifestations 10

  11. X-linked human genes - Examples Generalized Hypertrichosis - X-linked dominant 11

  12. X-linked human genes - Examples X-linked dominant faulty enamel All daughters with affected father will inherit and express the trait. 12

  13. X-linked human genes - Examples X-linked recessive Hemophilia in descendents of Queen Victoria - germline mutation 13

  14. Y-linked human genes - NCBI Map Viewer Many in Pseudoautosomal Region - nonfunctional SHOX - short stature 14

  15. Y-linked human genes - Examples SRY, Y-blood type antigen, Hairy Pinnae? Anthony Victor Guinness record 15

  16. Inheritance of X-linked traits Crisscross pattern of inheritance: Son inherits only X from mother (hemizygous) Daughter inherits one X from each parent (homozygous, heterozygous) 16

  17. Inheritance of X-linked traits Reciprocal Crosses: Sons inherit and express trait from mother 17

  18. Inheritance of X-linked traits F1 x F1 Crosses: 18

  19. Sex-Influenced Dominance Horns in sheep X LILI X X LRLR X Y LILR X X LILR X Y F2 Ratio: 1 LILI : 2 LILR : 1 LRLR 19

  20. Sex-Limited Dominance Milk production in cattle Beard attributes in humans Feather colors in birds 20

  21. Nondisjunction of Sex Chromosomes during Meiosis Failure to Segregate - Aneuploidy in offspring 21

  22. Nondisjunction Example in Drosophila XXX and Y die XO male, XXY female 22

  23. Nondisjunction Example in Drosophila Gametes with XX and XY 23

  24. Nondisjunction Examples in Humans Turner Syndrome (XO) 1 in 10,000 females born 90% die before birth Short, weblike necks, barrel chest, poor breast development, often infertile less ability spacial relationships 24

  25. Nondisjunction Examples in Humans Klinefelter Syndrome (XXY) Also XXXY, XXYY, etc. 1 in 1,000 males born Underdeveloped testes, taller than average, 50% some breast development, some subnormal intelligence 25

  26. Nondisjunction Examples in Humans XYY Syndrome 1 in 1,000 born Often taller than average Some reduced fertility 26

  27. Dosage Compensation in Mammals X-linked genes - Most needed for both sexes X inactivation - Barr body - Random in each cell of embryo 16 day, 500-1000 cells normal female XX normal male XY 27

  28. Dosage Compensation in Mammals 28

  29. Dosage Compensation in Mammals Heterozygous XAXa females - Mosaic Calico Cat Sweat glands orange/black absent 29

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