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 Sexual Differences - Human Chromosomes

3 Sexual Differences - Drosophila Chromosomes

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

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 Sexual Determination in Various Species

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

9 X-linked human genes - NCBI Map Viewer

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

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

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

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

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

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

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

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

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

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

23 Nondisjunction Example in Drosophila Gametes with XX and XY

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

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, cells normal female XX normal male XY

28 Dosage Compensation in Mammals

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