Microsoft Word - Genetics Problems.doc
Genetics 1
Neatly write your answers on a separate sheet of paper. Show your work. You must
specify the genotype or phenotype the numbers refer to in your ratios. Ex: 1:2:1 is not
sufficient. 1AA : 2Aa : 1aa (genotype) or 1 red : 2 pink: 1 white (phenotype) is co
ect
Assume the genes are autosomal unless otherwise specified.
1. In humans, the allele for albinism is recessive to the allele for normal skin
pigmentation. If two heterozygotes have children, what is the chance that a child will
have normal skin pigment? What is the chance that a child will be albino? If the child is
normal, what is the chance that it is a ca
ier (heterozygous) for the albino allele?
2. In purple people eaters, one-horn is dominant and no horns is recessive. Show the
cross of a purple people eater that is heterozygous for horns with a purple people eater
that does not have horns. Write the expected genotypic and phenotypic ratios of their
offspring.
3. In humans, the
own-eye (B) allele is dominant to the non-
own eye allele (b). (Eye
color is actually quite complicated and not well understood yet.) If two heterozygotes
have a child, what are the expected genotypic and phenotypic ratios of their offspring?
4. In seals that gene for the length of whiskers has two alleles. The dominant allele (W)
codes long whiskers and the recessive allele (w) codes for short whiskers. What
percentage of offspring would be expected to have short whiskers from the cross of two
long-whiskered seals, one that is homozygous dominant and one that is heterozygous?
5. In pea plants the yellow color allele (Y) is dominant over the green color allele (y) for
seed color and the tall allele (T) is dominant over the short allele (t) for plant height.
They are independently assorting genes. Parents heterozygous for both traits are cross-
pollinated. Using a 16 square Punnett square, determine the frequency for the four-
different phenotypes of the offspring.
6. Now let’s try a shortcut way of solving that same dihy
id cross. Because of Mendel’s
Law of Independent Assortment, we can work with the color gene and the height gene
separately. Set up two separate monohy
id crosses from those same parents. Then use
the laws of probability to calculate your frequencies (fraction) of each trait alone and
combined (multiply the fractions) and fill in the table.
Height Color = Probability
Tall, yellow
Tall, green
Short, yellow
Short, green
Genetics 2
Follow the directions from Genetics 1. Assume the genes are autosomal unless otherwise
specified.
1. In radishes, the gene that controls color exhibits incomplete dominance. True-
eeding red radishes crossed with true-
eeding white radishes combine to make purple
adishes. What are the genotypic and phenotypic ratios when you cross a purple radish
with a white radish?
2. Certain
eeds of cattle show incomplete dominance in coat color. When true-
eeding red cattle are
ed with true-
eeding white cattle, the offspring are roan
(pinkish coat color). Write the expected genotypic and phenotypic ratios of the offspring
when a roan cow is mated with a roan bull.
3. The cattle have a second gene for horned vs. hornless cattle. The allele for horns is
dominant. If a bull and cow are heterozygous for both the horn and the coat color genes,
what is the probability for each possible phenotype?
4. A man with type AB blood ma
ies a woman with type B blood. Her mother has type
O blood. Write the expected phenotypic and genotypic ratios of their children.
5. The father of a child has type AB blood. The mother has type A. Which blood type(s)
can their children NOT have? Why?
6. A woman with type A blood and a man with type B blood could potentially have
offspring with what blood types?
7. The mother has type A blood. Her husband has type B blood. Their child has type O
lood. The husband claims that the child can’t be his. Is he right? Explain.
8. The mother has type B blood. Her husband has type AB blood. Their child has type
O blood. The husband claims the child can’t be his. Is he right? Explain.
9. The mother has type AB blood. The father has type B blood. His mother has type O
lood. What are all the phenotypic possibilities of blood types for their children?
10. Achondroplasia (dwarfism) is caused by a dominant gene. A woman and man both
with dwarfism have children. Homozygous achondroplasia results in death of em
yos.
Write the expected genotypic and phenotypic ratios of live-birth offspring.
11. Hemophilia is a recessive disorder whose defective gene is located on the X
chromosome. List the expected genotypic and phenotypic ratios of the children from a
man normal for blood clotting and a woman who is a ca
ier of the defective blood
clotting allele. Report the ratios for boys separate from the ratios for girls.