HONORS Practice Genetics Problems
Mix of Complete and Complex Inheritance
1.
If two fruit flies, heterozygous for genes of one allelic pair, were bred together and had 200
offspring,
a. About how many would have the dominant phenotype?
b. Of these offspring, some will be homozygous dominant and some heterozygous. How is
it possible to establish which is which?
2.
Two mice with long tails were mated. The offspring consisted of 32 mice with long tails and
nine mice with short tails. We can determine that ______ is the dominant trait, and given that L
represents long tail and l represents short tails the genotype of each parent was _______.
3.
Vitamin D resistant rickets is produced by an X-linked dominant allele. Two recessive alleles
together will lead to normal bone development. What are the expected results from the
following crosses?
A.
A normal woman and a man with vitamin D resistant rickets.
B.
A normal man and a woman with the condition who has a normal father.
4.
Red-green color blindness is a human recessive sex-linked trait. A man and a woman with
normal vision have a color blind son. What is the probability that their next child will also be a
color blind son?
A. 0
B. 1/8
C. 1/4
D. 1/2
E. 3/4
5. Freckles is dominant, no freckles recessive. A man with freckles and a woman with no freckles
have three children with freckles and one with no freckles. What are the genotypes of the
parents and children?
6.
Imagine that you are a genetic counselor, and a couple that is planning to have children comes
to you for advice. Diane’s brother has hemophilia. There is no history of hemophilia in Craig’s
family. What is the probability that their child will have hemophilia? (recall that hemophilia is
caused by a sex-linked recessive allele).
7.
In humans, Albinism is caused by a single gene. The recessive allele (a), when homozygous,
results in no pigmentation in the skin and therefore a very pale skin. Ann Smith is an albino.
She marries Mike Jones, and they had two kids, Sara who has normal pigmentation, and Martha
who is albino.
A. What are the genotypes for each
Ann ______
Mike ______
Sara ______
Martha ______
B.
What is the probability that their next child would be albino? ______
C.
What is the probability that if they have two more children, that both children will be
normally pigmented? _______
D. If they have two more children what is the probability that one will be albino and one will be
normally pigmented? _______
8.
Matching. Match the description or example with the inheritance pattern.
A.
B.
C.
D.
E.
Codominance
Sex-linked recessive
Sex-linked dominant
Incomplete dominance
Complete dominance (mendelian dominance)
_____ Colorblindness and hemophilia are inherited as this
_____ a red snapdragon crossed with a white snapdragon produces pink flowers
_____ Hypercholesterolemia is a disorder in which the heterozygote has a reduced phenotype
compared with the homozygous recessive which is more severe
_____ Muscular Dystrophy occurs when a male has a recessive allele on his X chromosome
_____ In fruit flies, normal wings is dominant to vestigial wings (recessive). What a homozygous
dominant and a homozygous recessive are mated, they produce all normal individuals.