Name ___________________________________
Sex-linked and incomplete dominance problems
1.
A man is colorblind with the genotype XnY. The mother is not colorblind but carries a colorblind
allele. Give all the possible genotypes and phenotypes of their offspring.
2.
A couple are both phenotypically normal, but their son suffers from hemophilia, a sex-linked
recessive disorder. What fraction of their children is likely to suffer from hemophilia? What
fraction are likely to be carriers?
3.
Some cases of baldness are inherited as the result of an X-linked recessive allele (h). Charlie’s
dad was bald at 45, and Charlie (who is 38 ) wants to know if he should expect to lose his hair in
the next few years. Answer the following questions based on this information.
a. What is Charlie’s dad’s genotype? Does this tell you anything about Charlie’s
genotype?
b. Charlie’s mom, Gladys, has no signs of thinning hair, and neither did Gladys’ mom.
Gladys’ dad was bald, thought. what is Gladys’ genotype?
c. What are Charlie’s chances of going bald?
4.
In fruit flies, red eye color is a dominant sex-linked trait. When a white eyed female fly is mated
with a red-eyed male fly, all of the male offspring (F1) have white eyes and all of the female
offspring (F1) have read eyes. What offspring would be expected when male and female F1 flies
are mated? Indicate the genotypes, phenotypes and percentages.
5.
A cross between a blue blahblah bird and a white blahblah bird produces offspring that are
silver. The color of blahblah birds is determined by just two alleles.
a. What are the genotypes of the parent blahblah birds in the original cross?
b. What is the genotype of the silver offspring?
c. What would be the phenotypic ratios of offspring produced by two silver blahblah
birds?
6.
The color of fruit for plant “Z” is determined by two alleles. When two plants with orange fruits
are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50%
orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants?
7.
The inheritance of flower color in snapdragons illustrates incomplete dominance; When a red
snapdragon is crossed with a white one, all their offspring are pink. What offspring would be
produced, in what proportions, if two of these pink snapdragons were crossed? What offspring
would be produced, in what proportions, if a pink snapdragon was crossed with a white one?
8.
The inheritance of curly hair illustrates incomplete dominance: when a curly-haired individual
reproduces with a straight-haired one, the children all have wavy hair. What offspring would be
produced, in what proportions, when two people with wavy hair reproduce? When two people
with curly hair reproduce?