Sex-Linked Punnett Square Notes

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Sex-Linked Punnett Square Notes
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• What is this persons sex?

• female

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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

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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

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Examples of Sex-Linked Traits

• H Normal blood clotting
• h Hemophilia
• 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
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Sample Problems
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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
½ or 50
0/2 or 0
XHY
XhY
½ or 50
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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
½ or 50
XHY
XhY
½ or 50
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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
0/4 or 0
XHY
XHY
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A normal woman (whose father is a hemophiliac)
marries a hemophiliac man.

• What are their genotypes?

Her dad - XhY
XHX?
XhY
XHXh and XhY