1. A nonhemophiliac man marries a nonhemophiliac woman whose father was a hemophiliac. What kinds of children can they have and in what percentages?

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• 1. A nonhemophiliac man marries a nonhemophiliac
  woman whose father was a hemophiliac. What kinds
  of children can they have and in what percentages?

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Sex Linked Genetics 1
Step 1 Determine the letters you will use to
represent the alleles. For this one I chose B
for normal blood and b for the hemophiliac gene.
Step 2 Determine the alleles of the parents. The
non-hemophiliac man must be XBY. The
non-hemophiliac woman with a hemophiliac father
must be XBXb, because she had to get Xb from her
afflicted father.
Step 3 Set up your Punnett square and do the
cross. Determine the genotypes and expected
percent of each type of child from the cross.
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25 Normal girl 25 Normal boy 25 Carrier
girl 25 Hemophiliac son
XB
Y
XB
XB XB
XB Y
Xb
XBXb
Xb Y
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• 2. Two normal-visioned parents have a color-blind
  son. What are the genes of the parents? What
  are the chances of their having a color blind
  girl? Explain.

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Sex-Linked Genetics 2
Step 1 Choose your alleles. I will use C
for normal color vision and c for the red/green
color blind condition.
Step 2 Determine the genotypes of the parents.
Both parents have normal vision, yet they have a
color-blind son. Because, the dad can not have
the c allele (its sex-linked remember and he
has normal vision) the wife must be a carrier.
Dad XCY and Wife XCXc
Step 3 Set up your Punnett square and do the
cross!
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XC
Y
XC
XCXC
XCY
Xc
XCXc
XcY
There are no chances of this couple having a
color blind girl. The father would have to be
color blind to contribute the second defective Xc
allele needed to produce a color-blind daughter.
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• 3. A normal-visioned man marries a
  normal-visioned woman whose father was
  color-blind. They have two daughters who grow up
  and marry. The first daughter has five sons, all
  normal-visioned. The second daughter has two
  normal-visioned daughters and a color-blind son.
  Diagram the family tree, including the genes of
  all the people mentioned.

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Sex-Linked Genetics 3
Step 1 As this is another problem about color
blindness, we already have our alleles ready from
the previous problem. C for normal vision, c
for the red/green color blind condition. Use
what you know from the problem to assign
genotypes and do Punnett square crosses to help
answer all the questions. A family pedigree
might be a great way to show clearly the genes of
all the people mentioned.
Step 2 Figure out the genotypes of the
parents. Both have normal vision, so the man
must be XCY . The womans father was color blind
she has at least one daughter who has a color
blind son. That son had to get his Xc from his
mom who had to get it from her mom. So, the
woman must be a carrier. (XCXc)
Step 3 Do the crosses. Explain the expected
genotypes of all the people involved.
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XC
Y
Grandpa
Dad
Xc
Y


XC
XCXC
XCY


XC
XCXc
XCY
Xc
XcY
XCXc
XC
XCXc
XCY
Mom
These are their possible offspring. Moms dad
was color blind, so she got her Xc from him.
(see cross above) The problem says they had two
daughters, so we will focus on them. One
daughter had 5 sons, all with normal vision. She
must not be the carrier daughter, otherwise odds
are she would have had a color-blind son. Do we
know if her husband is color blind or not? The
other daughter had 2 normal vision daughters and
1 color-blind son, so she must be a carrier of
the Xc allele.
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The first daughter would have the genotype, XCXC
and all her sons would be XCY and they would have
normal vision. If her husband was color- blind
it would only effect their daughters, (50 would
be expected to be color-blind) but, because
they had no daughters we have no way of knowing
from this information if he is color-blind or
not. (see grandpa to see a Punnett square for
this situation.)
The second daughter would have to be the carrier.
Her daughters have normal vision. However, one
or both of them could be carriers of the trait.
The son, however, was not so lucky and got the
defective X. With no second X to mask the
effects, he will be color-blind.
XC
Y


XC
Normal vision
Normal vision
Xc
Color-blind son
Carrier
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Pedigree for this family
?