Human Sex Chromosomes & linked Genes Human chromosome condition: diploid(2n) = 46. 44 (22 pair) = autosomes 2 (1 pair) = sex chromosomes (Y chromosome = SEX IS MALE – it is physically missing part of the chromosome = less information)

MALE FEMALE

DOWN’S SYNDROME: NON-DISJUNCTION CHR. 21

X Y X X X X Y X X X Y X

46, XX Normal Female 0.511* 46, XY Normal Male 0.489* 45, XO Female 1/5,000 47, XXY Male 1/700 ‘Y’ chromosome = SEX IS MALE

Sex linkage is when a gene is carried on one of the sex chromosomes. Sex linked traits Are usually recessive (some are not) Are usually on the X Chromosome E.g.Hemophilia and Color Blindness

Genes On X and Y Chromosomes Are Not The Same

= XBXb = normal female “carrier” = XbXb = affected female = XBY = normal male = XbY =affected male G E N O T Y P S

ARE YOU COLOR BLIND?

ARE YOU COLOR BLIND?

ARE YOU COLOR BLIND?

ARE YOU COLOR BLIND?

HEMOPHILIA

Hemophilia: The “Royal Disease”

Other Sex linked Traits

MALE PATTERN BALDNESS

MUSCULAR DYSTROPHY (MDA)

MUSCULAR DYSTROPHY-MDA

E G G S S P E R M

DROSOPHILA - FRUIT FLIES X White Eye Male Red Eye Female r R X X R Y X

Y X X X X X Y X X X X Y F1: All Red Eyes White Eye Male Sperm r Red r Female Eggs R r X X R X X R Y r R X X R R X X Y

F1 Hybrid Cross R R X X r Y X

F2 : 1/2 The # Of Males Have White Eyes R Y X R X R R R X X X Y r r r R X X X Y X

DO A TEST CROSS WITH A WHITE EYED MALE HOW CAN YOU DETERMINE IF FEMALE FLY IS A ‘CARRIER’ OF WHITE EYE GENE OR NOT? DO A TEST CROSS WITH A WHITE EYED MALE