1. 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)

2. MALE
FEMALE

3. DOWN’S SYNDROME: NON-DISJUNCTION CHR. 21

4. X Y X X X X Y X X X Y X

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

7. 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

8. Genes On
X and Y
Chromosomes
Are
Not The Same

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

10. ARE YOU COLOR BLIND?

11. ARE YOU COLOR BLIND?

12. ARE YOU COLOR BLIND?

13. ARE YOU COLOR BLIND?

14. HEMOPHILIA

15. Hemophilia: The “Royal Disease”

17. Other Sex linked Traits

18. MALE PATTERN BALDNESS

19. MUSCULAR DYSTROPHY (MDA)

20. MUSCULAR DYSTROPHY-MDA

21. E G G S S P E R M

22. DROSOPHILA - FRUIT FLIESX
White Eye Male
Red Eye Female r R X X R Y X

23. 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

24. F1 Hybrid Cross R R X X r Y X

25. F2 : 1/2 The # Of Males Have White EyesR Y X R X R R R X X X Y r r r R X X X Y X

26. 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