Name:______________________________
Date:_____________ Period:____
Sex Linked Genes: Looking In-Depth at Hemophilia
Directions: Read the information below and complete the problems on this sheet.
One example of a sex-linked trait is the blood disorder called hemophilia. Normally when a
blood vessel is ruptured, such as when a wound in the skin occurs, the
wound bleeds, but then the blood clots and a scab is formed. People who
have hemophilia are unable to make certain proteins necessary for blood
to clot properly. When cuts and other injuries are obtained, bleeding is
difficult to stop without medical treatment. Hemophilia is a recessive trait
carried on the X chromosome only. Xh represents the recessive allele for
hemophilia and XH represents the dominant allele for NO disease.
Females can be a carrier of the trait without actually suffering from the
disorder. This means that a carrier has one dominant and one recessive
allele. However, a male that receives the trait on the X chromosome will
have the disorder. Males can not be carriers.
1. Indicate whether each person is HEALTHY or has HEMOPHILIA.
a.
b.
c.
d.
e.
Female with genotype XH Xh
Female with genotype XH XH
Female with genotype Xh Xh
Male with genotype
XH Y
Male with genotype
Xh Y
_________________
_________________
_________________
_________________
__________________
2. Complete the Punnett Square shown here where Xh represents the recessive allele for
hemophilia and XH represents the dominant allele for NO disease.
XH
Xh
XH
Y
a. What percentage of the children will have hemophilia? _________
b. Are the children with hemophilia male or female? __________
c. What percentage of the children will be carriers? (HINT: A carrier is a person with
one healthy allele and one hemophilia allele.) __________
CONTINUE ON BACK…
Assignments
Name:______________________________
Date:_____________ Period:____
3. Complete the Punnett Square shown here where Xh represents the recessive allele for
hemophilia and XH represents the dominant allele for NO disease.
XH
Xh
Xh
Y
a. What percentage of the children will have hemophilia? _________
b. What percentage of the children will be carriers? (HINT: A carrier is a person with
one healthy allele and one hemophilia allele.) __________
4. A husband and a wife have 3 children: two boys and one girl. The girl has hemophilia
while both boys are normal. What are the genotypes of mom and dad? (HINT: Look
at the Punnett Square results in Question #2 and in Question #3. Find the
Punnett Square that matches the information given in this problem. Once you
find the matching square write down the genotype of mom and dad in the space
below.)
Mom- _________
Dad - ___________
Assignments