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Name: ________________________________________________ Date: _________________________
Sex Linked Traits: Punnetts and Pedigrees
Fur color in cats is a sex-linked trait. The X chromosome can code
for black fur (XB) or orange fur (XO). The Y chromosome does not
contain a gene for fur color. A cat with a both alleles will have the
calico fur color (black, orange and white spots).
1. A black female cat and an orange male cat have 8 kittens. Draw a Punnett square to show this
cross, then fill in the table. You may distribute the number of kittens as you wish.
a. List all of the possibilities in the data table below
Genotype
Phenotype
Gender
Percentage
# of kittens
1
2
2. Now, one of the calico female offspring from Question #1 mates with a black male cat. They had 4
kittens. Fill in the data table with the correct possibilities.
a. List all of the possibilities in the data table below
Genotype
Phenotype
Gender
Percentage
# of kittens
1
2
3
4
3. Draw a pedigree tree below for the cats from Questions #1 and #2. Note the key indicating that
females are circles and males are squares. Shade the circle or square completely for black cats,
leave it white for orange cats, and half-shaded for calico.
a. Drawing of pedigree
Key
Female Black
Female Orange
Female Calico
Male Black
Male Orange
Male Calico
4. From your pedigree tree answer the following questions:
a. How many cats are calico males? _____ calico females? _____
b. How many cats were orange males? _____ orange females? _____
c. Can there be calico male? Explain:
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5. Hemophilia is an sex-linked recessive disorder. A mother who is a carrier wants to know if there is a
chance that her daughters will have the disorder. Her husband does NOT have hemophilia. Draw a
Punnett square below to show there possible offspring. XH = Normal Blood, Xh = Hemophilia, Y =
contains no blood genes.
Are any of there three daughters inflicted with the disorder hemophilia? ___________________________
Why or why not? _________________________________________________________________________
o
o
o
o
Each of the three daughters finds a mate.
The first couple has two normal daughters and one normal son.
The second couple has no children.
The third daughter mates with a normal man. They have 2 daughters who are both normal and two
sons, one with hemophilia and one without hemophilia.
o Draw a pedigree tree and symbols for the key. Make sure to label each with a genotype.
Pedigree:
Key
Female Hemo
Female Normal
Female Carrier
Male Hemo
Male Normal
Male Carrier
6. In fruit flies, the gene for white eyes is sex-linked recessive. (XR) is red and (Xr) is white. Cross a
white-eyed female with a normal (homozygous) red-eyed male.
a. What percent of the males will have red eyes? ____White eyes? ____
b. What percent of the females will have red eyes? ___White eyes? ____
c. What total percent of the offspring will be white-eyed? _______
d. What percent of the offspring will be carriers of the white eye trait? ______
7. Using the same information as for Question #6, cross a heterozygous red-eyed female with a redeyed male.
a. What are the genotypes of each parent? ______
b. What fraction of the children will have red eyes? _______
c. What fraction of the children will have white eyes? _______
d. What fraction of the female children will carry the white eyed trait? ________
e. What does the term carrier mean?
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