Name
Period
Date
/
/
Basic Genetics Practice Problems
P = purple flowers (dominant)
T = tall (dominant)
Y = yellow seeds (dominant)
R = round seeds (dominant)
p = white flowers (recessive)
t = dwarf (recessive)
y = green seeds (recessive)
r = wrinkled seeds (recessive)
1: If you cross two heterozygous plants with purple flowers, what are the genotypes
and phenotypes of the progeny, and in what ratios?
2: Star-bellied sneetches have bellies with stars, but plain-bellied sneetches
have none upon thars. A star on a sneetch belly is due to a recessive allele.
Perform a cross between a Pp sneetch and a pp sneetch.
3: If you cross a homozygous plant that has round seeds with a plant that has wrinkled seeds, and then cross
the offspring to another plant with wrinkled seeds, what is the chance you will get plants with wrinkled seeds
from this second cross?
5: When crossed with a solid-colored rabbit, a spotted rabbit produced all spotted offspring. When the
offspring rabbits were crossed among themselves, they produced 32 spotted and 10 solid-colored rabbits.
How many of the spotted rabbits of the 32 in the third generation of this problem would be expected to be
homozygous? How many of the 10 solid-colored rabbits would be homozygous?
6: Human blood type is determined by a gene with three possible alleles. What are the chances of a Type-AB
male and a Type-O female having a child with Type-B blood?
7: A thoroughbred stallion is mated with three different mares. The following are the results in terms of coat
color. Choose a letter to use to symbolize the alleles for this gene, and fill in blanks with likely genotypes.
STALLION (♂)
GENOTYPE
MARE (♀)
GENOTYPE
OFFSPRING PHENOTYPES
White
_______
#1-Black
_______
½ Black, ½ White
#2-White
_______
All White
#3-White
_______
¼ Black, ¾ White
8: A baby girl was born in the days before DNA testing. The mother did not know who the father was, but she
may have narrowed it down to three possibilities. Free earlobes are dominant to attached, and long 2 nd
toe is dominant to long great toe.
Mother = Free Earlobes, Long Great Toe
Child
= Attached Earlobes, Long 2nd Toe
Mark
Kerry
Matt
Potential Fathers
=
Free Earlobes, Long 2nd Toe
=
Free Earlobes, Long Great Toe
=
Attached Earlobes, Long 2nd Toe
Who is the father? Circle the names of ALL possibilities. If none of the above are possible, circle none of them.
9: Use a Punnett square to determine the offspring genotypes and phenotypes (and their frequencies) from
the following cross between two pea plants.
RrYy x RrYy