Homework set 3: Genetics Homework 2
Name:
All work must be shown to get credit, please BOX your answer where appropriate.
1. In a cross with homozygous dominant and
homozygous recessive parents (P-generation),
what proportion of the offspring in the F-2
generation (if you self-cross the F-1 Generation)
would exhibit the phenotypic characteristic of the
recessive parent?
2. In a test cross, the individual with the unknown
genotype is crossed with an individual with what
genotype?
3. In human blood types, which blood type best
represents codominance?
4. Which human blood type allele is recessive to two
different alleles?
5. In snapdragons the two alleles for flower color
belong to one gene and this gene exhibits
incomplete dominance. What will be the
phenotypes of a cross of a red snapdragon with a
white snapdragon?
6. Albinism is an autosomal recessive trait. A normally
pigmented man marries an albino woman. If their
first child was an albino what would their (the
parents) genotypes and their child's genotype be?
If they have more children what other genotypes
could there be?
7. An albino man marries normally pigmented woman.
They have 13 children all of whom are normally
pigmented. What are the probable genotypes of
the children and parents?
8. A normally pigmented marries an albino woman.
The man's father was an albino. The woman's
parents were both normally pigmented. The man
and woman have three children, two normally
pigmented and one albino. List each of these
persons and give their probable genotypes.
In Drosophila, the fruit fly, wild type long wings "G" is
dominant over vestigial wing (g).
9. In a cross between heterozygous long-winged male
and a vestigial-winged female, what types and
proportions of genotypes would be expected?
10. In a cross between two heterozygous long-winged
flies, what types and proportions of genotypes
would be expected?
11. If a heterozygous long-winged fly mated with a
homozygous long-winged one, what percentage of
the offspring would be expected to be homozygous
long-winged? Would there be any vestigial-winged
flies?
12. A long-winged fly mated with a vestigial-winged fly
producing 35 long-winged and 35 vestigial-winged
offspring. What are the genotypes of the parents?
Of the long-winged offspring? Of the vestigialwinged offspring?
13. Mating a long-winged fly with a vestigal-winged fly
produced 256 offspring all of which were longwinged. What were the probable genotypes of the
parents? Mating of the F1 long-winged flies
together would produce what types of offspring
genotypically and in what proportions?
14. In human beings, a downward-pointed frontal
hairline ("widow's peak") is a heritable trait. A
person with widow's peak always has at least one
parent who also has this trait, whereas persons
with a straight frontal hairline may occur in families
in which one or even both parents have widow's
peaks. When both parents have a straight frontal
hairline, all children also have a straight hairline.
Using A and a to symbolize alleles for this trait,
what is the genotype of an individual without
widow's peak? (Show your reasoning)
15. The first of three children of two normally
pigmented parents has albinism, a recessive trait
that results from lack of the pigment melanin.
a. Given that the normal allele is A and the albino
allele is a, draw this pedigree and label both the
phenotypes and genotypes.
b. What is the probability that the second child,
who shows normal pigmentation, is a carrier?
c. What is the probability that both unaffected
children are carriers? INCLUDE LOGIC
STATEMENT(s)
d. What is the probability that only one of the two
unaffected children is a carrier? INCLUDE LOGIC
STATEMENT(s)