Sex-Linked Punnett Square Notes - Copy_064734.ppt

This is a PowerPoint presentation about sex linked trait which includes sample punnett square and also the genetic traits that are passed on to the next generations.

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. 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 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.
Males will express whether it is dominant or
recessive
Females can be carriers and not show
One X is normal and suppresses the recessive trait
 

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. All genotypes in sex-linked
problems must have chromosomes

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

16. 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:
X
H
Y
X
h
Y
X
H
X
H

X
h
X
h

X
H
X
h

17. Sample Problems

18. 1. X
H
X
h
x X
H
Y
Chances of:
a. hemophiliac
child?
b. hemophiliac
son?
c. hemophiliac
daughter?
d. daughter
who is carrier?
X
H
X
H
X
H
Y X
h
Y
X
H
X
h
X
H
Y
X
H
X
h
¼ or 25%
25%
0%
25%

19. 2. A woman who is a carrier for
hemophilia marries a hemophiliac man.
Chances of:
a. hemophiliac
child?
b. hemophiliac
son?
c. hemophiliac
daughter?

20. 3. A normal man marries a Homozygous
normal woman.
Chances of:
 a. Will any of
their kids be

hemophiliacs?

21. BLOOD TYPING
There are 3 alleles of the gene that
controls blood type: I
A
, I
B
, i The I
stands for immunoglobin.
I
A
and I
B
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.

22. Possible genotypes are as follows:
Genotypes Blood type
I
A
I
A
or I
A
i A
I
B
I
B
or I
B
i B
I
A
I
B
AB
ii O

23. 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 I
A
I
B
I
B