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Human Genetics: Sex-Linked Traits 1
Ch. 14
Practice with Genotypes and Phenotypes for X-linked Traits
Name: ____________________ Per:___ COOK
Fill in the correct information for the questions below. Remember, these are sex-linked traits so you MUST include the X
and Y in the genotype. If these questions were for AUTOSOMAL traits you would NOT use X and Y. If the statement is
not genetically possible, write NP in the blank.
Part I. If T is the allele for tallness and t is for shortness, what is the genotype of a plant that is…….
1. homozygous tall? _____
3. homozygous short? ______
2. heterozygous tall? _____
4. heterozygous short? ______
What is the phenotype of… 5. genotype XX ? ______________
6. genotype XY? _______________
Part II. If R is the allele for a normal gene, and r is for Anhidrotic Ectodermal Dysplasia (a sex-linked trait), what is the
genotype of a……
7. heterozygous female? ________
11. male carrier? __________
8. homozygous dominant female? ________
12. normal male? __________
9. homozygous recessive female? _________
13. male with dysplasia? ________
10. female carrier? __________
Part III. If R is the allele for a normal gene, and r is for Anhidrotic Ectodermal Dysplasia (a sex-linked trait), what is the
phenotype (including sex) of a person with genotype…..
14. XRXr ?________________________________
17. XRY ?_______________________________
15. XrXr ?_________________________________
18. XrY ?_______________________________
16. XRXR ?________________________________
19. XrYr ? _______________________________
Part IV. If D is an allele for a normal gene, and d is for muscular dystrophy (a sex-linked trait), what is the genotype of
a……..
20. homozygous recessive female? _________
23. female carrier? __________
21. Recessive male? __________
24. male carrier? ___________
22. Dominant male? __________
Part V. If D is an allele for a normal gene, and d is for muscular dystrophy (a sex-linked trait), what is the phenotype
(including sex) of a person with genotype…..
25. XDXD ?_______________________________
27. XDY ? _______________________________
26. XDXd ? _______________________________
28. XdY ? _______________________________
Part VI.
29. Write (in words) what it means if a person is homozygous for a sex-linked trait, then write the letters for a pair of
homozygous alleles using your first initial.
30. Write (in words) what it means if a person is heterozygous for a sex-linked trait, then write the letters for a pair of
heterozygous alleles using your first initial.
31. Can a male be a carrier? (Yes or No)
32. Why?
Human Genetics: Sex-Linked Traits 1
Ch. 14
Human Genetics Punnett Squares: Remember: for genotypes write both alleles and sex chromosomes – i.e. XNXN
Do Punnett Squares on Separate sheet of notebook paper.
1. A color-blind (XnXn) woman marries a man with normal (XNY) vision.
What genotype and phenotype ratios do you expect from the offspring?
# of color-blind males: ________________
# of color-blind females: _______________
2. Hemophilia (h) is recessive to normal blood clotting (H). If a woman who is not a carrier for hemophilia (XHXH )
marries a man who is a hemophiliac (XhY),
What percentage of their male offspring would you expect to be hemophiliacs? _____%
3. Muscular dystrophy (d) is a recessive disorder. A woman who is a carrier (XDXd) marries a normal man (XDY),
What % of daughters have muscular dystrophy? __________%
4. Anhidrotic ectodermal dysplasia (AED) is sex-linked; it’s caused by an inactive X chromosome. Men with this trait
lack teeth, sweat glands, and have very little body hair. Women who carry AED lack some teeth, have thin hair, and
are missing sweat glands from patches of their skin.
a. If a man with AED (XaY) and a carrier woman (XAXa) have children, what % of their sons will have AED? _______%
b. What % of daughters will have AED?_________%
c. What % of sons will NOT have AED? __________%
d. Will any daughters be carriers? _____
e. If so, how many? ________
5. The bison herd on Konza Prairie has begun to show a genetic defect. Some of the males have a condition known as
"rabbit hock" in which the knee of the back leg is malformed slightly. This condition is controlled by a sex-linked
gene and it is recessive. Now, suppose that the herd bull (the dominant one which does most of the breeding) who
is normal (XN) mates with a cow that is a carrier for rabbit hock.
a. What are his chances of producing a normal son (bull)?
b. If he mates with this cow every year, what percentage of their daughters will have normal knees?
c. What percentage of their daughters will be carriers of rabbit hock?
6. Red-green color blindness (b) is a recessive sex-linked trait. A colorblind male marries a normal female. Their
daughter is colorblind.
a. What are the genotypes of both parents and the daughter?
b. Can a colorblind father have daughters who are not colorblind? Explain.
c. If a normal sighted woman whose father was color-blind marries a color-blind man, what is the probability that
they will have a colorblind child?
7. Clouded leopards are a medium sized, endangered species of cat, living in the very wet cloud forests of Central
America. Assume that the normal spots (XN) are a dominant, sex-linked trait and that dark spots are the recessive
counterpart. Suppose as a Conservation Biologist, you are involved in a clouded leopard breeding program. One year
you cross a male with dark spots and a female with normal spots. She has four cubs and, conveniently, two are male
and two female. One male and one female cub have normal spots and one each have dark spots.
a. What is the genotype of the mother?
b. Suppose a few years later, you cross the female cub that has normal spots with a male that also has normal spots.
How many of each genotype will be found in the cubs (assume 4)?
c. Will any of the cubs from this latest cross have dark spots?
d. If so, how many and of what sex will they be?