Genetics Practice Problems and Study Guide
Biology
Dr. Altstiel, Room 107
1.
In your own words, define the following terms: genotype, phenotype, homozygous, heterozygous,
alleles, monohybrid cross, Punnett square.
2.
What is a purebred stock?
3.
In guinea pigs, the allele for a black coat is dominant to the allele for a white coat. A black guinea
pig was crossed with a white guinea pig. The F1 offspring has a black coat. Describe how you could
determine whether or not the black parent is homozygous or heterozygous for the condition.
Indicate the letter you will use to represent an allele. What is the probability that the parent is
homozygous for black? Use a Punnett square.
4.
For Labrador retrievers, black fur color is dominant to yellow. Explain how a homozygous black dog
has a different genotype than a heterozygous black dog. Could the heterozygous black dog have the
same genotype as a yellow-haired dog?
5.
A pea plant with round seeds is cross-pollinated with a pea plant that has wrinkled seeds. For the
cross, indicate each of the following:
a.
b.
c.
d.
the genotypes of the parents if the round-seeds plant were heterozygous
the gametes produced by the round and wrinkled-seed parents
the genotypes and the phenotypes of the F1 generation
The F2 generation, if two round plants from the F1 generation were cross-pollinated
6.
For Dalmatian dogs, the spotted condition is dominant to non-spotted. Using a Punnett square, show
the results of a cross between two heterozygous parents. A spotted female Dalmatian dog mates with
an unknown father. From the appearance of the pups, the owner concludes that the male was a
Dalmatian. The owner notes that the female had six pups, three spotted and three non-spotted. What
are the genotype and phenotype of the unknown male?
7.
For Mexican hairless dogs, the hairless condition is dominant to hairy. A litter of eight pups is
found; six are hairless and two are hairy. What are the genotypes of their parents?
8.
A human neurological disorder, referred to as Huntington’s disease, is caused by a dominant gene.
Because the gene doesn’t express until a person reaches about 50 years of age, early detection has
been difficult. A woman whose father had Huntington’s disease begins to show symptoms. Her
husband shows no symptoms, nor does anyone in his immediate family. The woman’s father had
Huntington’s disease, but her mother never developed the disorder.
a. What is the genotype of the woman who has developed Huntington’s disease?
b. What is the probable genotype of the woman’s husband?
c. If the woman has 6 children, how many are likely to develop Huntington’s disease?
9.
Diabetes is caused by a recessive genetic disorder. A defective gene reduces insulin production by
the pancreas. Insulin is released into the circulatory system and allows the cells of the body to absorb
glucose from the blood. Individuals who lack insulin have high blood sugar. In an attempt to trace
the inheritance of the defective gene in one family, the following data was gathered (Table 1).
Table 1
Name
Relationship
Phenotype
Jennifer
Mother
Normal
Ryan
Father
Normal
Walter
Son of Ryan and Jennifer
Diabetic
Susan
Wife of Walter
Normal
Helen
Daughter of Ryan and Jennifer
Normal
James
Son of Ryan and Jennifer
Normal
Colin
Son of Susan and Walter
Diabetic
A. Construct a pedigree chart showing the passage of the diabetic gene.
B. Indicate the probable genotypes for Jennifer and Ryan.
C. Indicate the probable genotypes for Susan and Walter.
10. Multiple alleles control the intensity of pigment in mice. The gene D1 designates full color, D2
designates dilute color, and D3 is deadly when homozygous. The order of dominance is D1>D2>D3.
When a full-color male is mated to a dilute-color female, the offspring are produced in the following
ratio: two full colors to one dilute color to one dead. Indicate the genotypes of the parents.
11. Palomino horses are known to be caused by the interaction of two different genes. The allele C r in the
homozygous condition produces chestnut, or reddish coat. The allele Cm in the homozygous condition
produces a very pale cream coat, called cremello. The palomino color is caused by the interaction of
both chestnut and cremello alleles. Indicate the expected ratios in the F1 generation from mating a
palomino with a cremello.