Sex-Linked Inheritance
Date ______
Name ___________________
Colorblindness is a recessive trait found on the X chromosome. In this investigation you will model
how sex-linked traits, such as colorblindness, are inherited.
A woman who is a carrier for colorblindness marries a colorblind man:


What is the genotype of the woman and the man?
Make a Punnett square to show the all possible
outcomes and give the phenotype ratio.
Obtain a two paper cups, one that says
“mom” and one that says “dad.” Use
beans to represent the X and Y
chromosomes. The white bean
represents the X chromosome and the
red bean represents the Y chromosome.
A dot on the white bean represents a
recessive allele for colorblindness.
Randomly pick one bean from each cup
to represent how each parent contributes
a sex chromosome to a fertilized egg.
In your data table, record the color of
each bean and the sex of the individual
who would carry this pair of
chromosomes. Also record how many Xlinked alleles the individual has. Put the
beans back in the cups they came from.
Repeat this process until you have
completed 12 trials.
Trial #
Sex
Chromosomes
(XX or XY)
Number of
Colorblindness
Alleles
Is the
individual
colorblind (Yes
or No)
1
2
3
4
5
6
7
8
9
10
11
12
Analysis
____________________
What is the actual number of males and females after 12 trials? ___________________
What is the expected number of colorblind males and females for 12 trials? ____________
What is the actual number of colorblind males and females after 12 trials? ____________
1. What is expected number of males and females for 12 trials?
2.
3.
4.
5. Compare your actual and expected numbers for color males and females. Do they agree or
disagree? If they disagree, how much do they disagree? What could you do to get closer to the
______________________________________________
_________________________________________________________
expected results?
6. How would the results be different if the man was not colorblind? Use a Punnett square to
support your explanation.
Date ______
Sex-Linked Inheritance
Name ___________________
Hemophilia is a sex-linked trait. Use the following symbols to answer the questions.
XHXH = normal female
XHXh = normal female, a “carrier” of the trait
XhXh = hemophiliac female
XHY = normal male
XhY = hemophiliac male
1. Queen Victoria in England was a carrier for hemophilia. Draw a Punnett Square for the cross
between her and her husband if her husband did not have hemophilia.
a. What is the probability that the couple will have a female with hemophilia?
b. If the couple has a male son, what is the probability that he will have hemophilia?
2. If a female has hemophilia, what must be the genotypes of her parents?
3. A homozygous normal female marries a male with hemophilia. What percentage of their sons will
have hemophilia? What percent of their daughters will be carriers for hemophilia?
4. A normal male marries a normal female and they have 24 children. They have 12 daughters who
are all normal, 6 sons who are normal, and 6 sons who have hemophilia. Explain these results.
5. In humans, normal vision (XC) is dominant to colorblindness (Xc) and is sex-linked. A normalvisioned man, whose father was colorblind, marries a colorblind woman. What are the chances that
a son will be colorblind? A daughter? Explain.
6. Hairy ear rims is a trait carried on the Y chromosome. A woman does not have hairy ear rims, and
her husband does.
a. Draw a Punnett Square for the cross.
b. What is the probability of the couple having a child with hairy rims?
c. If a woman does not have hairy rims, and her husband does not have hairy ear rims, what is
the probability that they will have a child with hairy ear rims?