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Name:_____________________________ Date:____________ Period:________
Hemophilia
Why are there more colorblind men than colorblind women? Certain traits are controlled by gene
located on the sex chromosomes, usually the X chromosome. These traits are called SEX-LINKED
TRAITS. This activity will help you understand how human sex-linked traits are passed from one
generation to the next.
Hemophilia is a recessive disorder caused by a mutation on the X chromosome. The dominant allele
codes for a protein that helps clot the blood. Clotting blood is necessary to seal and heal cuts. The
recessive allele codes for a defective protein, and the person with this faulty protein risks bleeding to
death even from minor cuts or internal bruises.
All X chromosomes have locations for the genes for hemophilia, as well as color-blindness and other
sex-linked traits. Therefore, we still use the system of letters, such as E and e, to represent forms of
these genes as superscripts on the X chromosome. For example, the normal gene for blood clotting is
XH, and the defective recessive gene is Xh.
Because the gene is located on the X chromosome, females have two hemophilia genes and males
have one. Heterozygous females have one recessive copy of the gene, but do not have the disease.
They are called carriers because they are able to pass the gene on to their offspring.
1. Define SEX-LINKED TRAITS:
2. Complete the symbols for the Hemophilia alleles: dominant X
recessive X
3. Sons inherit the ______ chromosome from their mother and the ______ chromosome from
their father. Daughters inherit the ______ chromosome from their mother and the ______
chromosome from father.
Genotype
4. Fill in the phenotype for each genotype.
5. Circle the carrier genotype from the list of
genotypes in the chart.
XH XH
Xh Xh
XH Y
Xh Y
XH Xh
Phenotype
Sex
Hemophilia?
(M or F)
(Y or N)
6. Use a Punnett square to determine the possible offspring that a carrier female and a
hemophiliac male will have.
a. What percent chance do they have of getting a daughter with hemophilia? _________
b. A son with hemophilia? ____________
7. Draw a Punnett square for each example. You may need more than one square for each.
a. Matings that will produce 100%
hemophiliac offspring.
b. Matings that will produce 100%
healthy offspring.