1. Sex-Linked Punnett Square Notes

2. Karyotype A photograph of a cell’s chromosomes arranged in pairs according to size

3. Normal Karyotype: 23 pairs of chromosomes
pairs 1-22 are autosomes
pair 23 are sex chromosomes
24-5

5. Sex Chromosomes X Y

6. some genes are unique only to the Y chromosome
X chromosome
has over 1,000 genes
most genes on the X chromosome do not have corresponding alleles on the Y chromosome
Y chromosome
has only a few dozen genes
some genes are unique only to the Y chromosome

7. Sex-Linked Traits
Those traits whose genes are found on the X chromosome but NOT on the Y chromosome

8. Examples of Sex-linked Traits:
Red-green colorblindness
Male Pattern Baldness
Hemophilia (Queen Victoria was a carrier)
Duchenne Muscular Dystrophy (fatal)

10. Color Blindness “tests”

11. The test below is simpler
The test below is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see
a 2 revealed in the dots.

12. Females = XX –carry 2 alleles for a sex-linked trait
Males = XY – only carry 1 allele for a sex-linked trait, so it is easier for them to get sex-linked diseases

13. Sex-Linked Traits, cont.
Males receive sex-linked traits from their mother because their mother gives them the X chromosome and their father gives them the Y chromosome

14. Example of Sex-Linked Trait
H = Normal blood clotting
h = Hemophilia

15. Example of Sex-Linked Trait
Normal male:
Male with Hemophilia:
Normal female (not a carrier for hemophilia – homozygous):
Normal female (carrier for hemophilia – heterozygous):
Female with Hemophilia:
XHY
XhY
XHXH
XHXh
XhXh

16. Sample Problems

17. 1. XHXh x XHY Chances of: a. hemophiliac child? b. hemophiliac son?
c. hemophiliac daughter?
d. daughter who is carrier?
¼ or 25%
XH Xh XH Y
XHXh
XHXH
25%
XHY
XhY 0%
25%

18. 2. A woman who is a carrier for hemophilia marries a hemophiliac man.
XHXh x XhY
Chances of:
a. hemophiliac child?
b. hemophiliac son?
c. hemophiliac daughter?
XH Xh
2/4 or 50% Xh Y
XhXh
XHXh
25%
XHY
XhY
25%

19. 3. A normal man marries a Homozygous normal woman.
XHXH x XHY
Chances of:
a. Will any of their kids be hemophiliacs?
XH XH XH Y
XHXH
XHXH
XHY
XHY
0/4 or 0%

20. BLOOD TYPING
There are 3 alleles of the gene that controls blood type: IA , IB , i The I stands for immunoglobin.
IA and IB are Co-Dominant genes, meaning when inherited together, they are both fully expressed, not blended, as in Incomplete Dominance. “ i ” is the recessive form of the allele.

21. Possible genotypes are as follows:
Genotypes Blood type
IAIA or IAi A IBIB or IBi B
IAIB AB
ii O

22. Draw a Punnett square showing all the possible genotypes for the offspring produced by a type “O” mother and a Type “AB” father.
Cross: ii x IAIB IB