Transcript Sex-Linked Punnett Square Notes

Sex-Linked Punnett
Square Notes
•What is this person’s sex?
•female
Sex-Linked Traits
 Those
traits whose genes are
found on the X chromosome but
NOT on the Y chromosome
 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
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
Examples of Sex-Linked Traits
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H = Normal blood clotting
h = Hemophilia
Normal male: XHY
Male with Hemophilia: XhY
Normal female (not a carrier for
hemophilia – homozygous): XHXH
Normal female (carrier for hemophilia
– heterozygous): XHXh
Female with Hemophilia: XhXh
Sample Problems
1.
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H
h
X X
x
Chances of:
a. hemophiliac
child? ¼ or 25%
b. hemophiliac
son? ½ or 50%
XH
c. hemophiliac
daughter? 0/2 or 0%
d. daughter
Y
who is carrier?
½ or 50%
H
X Y
XH
Xh
XHXH
XHXh
XHY
XhY
2. A woman who is a carrier for
hemophilia marries a hemophiliac man.
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Chances of:
a. hemophiliac
child? 2/4 or 50%
b. hemophiliac
Xh
son? ½ or 50%
c. hemophiliac
daughter?
Y
½ or 50%
XHXh x XhY
XH
Xh
XHXh
XhXh
XHY
XhY
3. A normal man marries a Homozygous
normal woman.
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Chances of:
a. Will any of
their kids be
hemophiliacs?
0/4 or 0%
XHXH x XHY
XH
XH
Y
XH
XHXH
XHXH
XHY
XHY
A normal woman (whose father is a
hemophiliac) marries a hemophiliac man.
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What are their genotypes?
Her dad - XhY
XHX?
XhY
XHXh and XhY