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Name: __________________________________ Date: _______________
Sex-linked Traits = any gene that is associated with the X or the Y chromosome
PROBLEM: Cross a female carrier for hemophilia with a male with hemophilia. H=normal, and h=hemophilia
(the allele for hemophilia is recessive)
STEP 1: Determine what kind of problem you are trying to solve.
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Does it involve simple dominant and recessive traits, Incomplete dominance, or Co-dominance?
Is it a monohybrid or dihyrid?
In this case there is only one trait..........this is a monohybrid cross involving sex linked traits.
STEP 2: Determine letters you will use to specify traits.
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In this case it is a sex-linked problem. Remember that XX is female, and XY is male. H=normal and
h=hemophilia.
STEP 3: Determine parents’ genotypes.
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In this case you were told the parents were: Female carrier =
XhX, and a male with hemophilia = XhY.
The Cross is: XHXh x XhY
STEP 4: Make your punnet square and make gametes (these go on the
top and side of your punnett square.
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XHXh would make a XH and Xh
XhY would make a Xh and Y
STEP 5: Complete cross and determine possible offspring.
STEP 6: Determine possible genotypes and phenotypes of offspring.
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Genotypic ratio: Make a list of all the different genotypes (the letter combinations) and determine how
many of each you have.
Phenotypic ratio: Make a list of all the different phenotypes (physical characteristics).
o In this problem this would be: Female Carrier = 1/4 (25%), Female w/ hemophilia = 1/4 (25%),
Normal male = 1/4 (25%), and Male w/ hemophilia = 1/4 (25%).
Answer the following questions based on this genetic cross:
1. Joe and Jane are expecting a daughter. What is the chance that she will have hemophilia? (Hint: since
she is a daughter, you are only considering those boxes that are female)
Sex-linked traits practice problems:
1. What are the sexes and eye colors of flies with the following genotypes:
X R X r _________________
X R X R _________________
X R Y _________________
X r Y _________________
2. What are the genotypes of these flies?
white eyed, male ____________
white eyed, female ___________
red eyed female (heterozygous) ________
red eyed, male ___________
3. Show the cross of a white eyed female X r X r with a red-eyed male X R Y .
5. Show the cross of a red eyed female (heterozygous) and a red eyed male. What are the genotypes of the parents?
___________ & ________________
How many are:
white eyed, male___white eyed, female ___
red eyed, male ____ red eyed, female ____
7. In humans, hemophilia is a sex linked trait. Females can be normal, carriers, or have the disease. Males will either
have the disease or not (but they won’t ever be carriers)
= female, normal
= male, normal
= female, carrier
= male, hemophiliac
= female, hemophiliac
8. A woman who is a carrier marries a normal man. Show the cross. What is the probability that their
children will have hemophilia? _______________ What is the chance that their SON will have hemophilia?
_______________ What is the chance that their DAUGHTER will have hemophilia? ________________