1. 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.

2. 2 Sexual Differences - Human Chromosomes

3. 3 Sexual Differences - Drosophila Chromosomes

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

5. 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

6. 6 Sexual Determination in Various Species

7. 7

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

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

10. 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

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

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

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

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

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

16. 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)

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

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

19. 19 Sex-Influenced Dominance Horns in sheep L I L I X X L R L R X Y L I L R X X L I L R X Y X F2 Ratio: 1 L I L I : 2 L I L R : 1 L R L R

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

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

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

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

24. 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

25. 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

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

27. 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

28. 28 Dosage Compensation in Mammals

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