DIHYBRID GENETICS PROBLEMS
Name
_________________________
1
In garden peas, tall (T) vine is dominant over short (t) vine, and round pea pod (R) is
dominant over wrinkled pea pod (r). Cross a homozygous tall, round pea plant with a
homozygous short, wrinkled pea plant. Show the genotypes and phenotypes of the F1
offspring, and the probability of each.
__________ Genotype of the homozygous tall, round pea plant
__________ Genotype of the homozygous short, wrinkled pea plant.
2
In garden peas, tall (T) vine is dominant over short (t) vine. Yellow (Y) seed color is
dominant over green (y) seed color. Cross a heterozygous tall, yellow seeded plant with a
heterozygous tall, yellow seeded plant.
______________________ Genotypes of the parent plants
_______ What is the probability for a tall offspring?
_______ What is the probability for a short offspring?
_______ What is the probability for a yellow offspring?
_______ What is the probability for a green offspring?
_______ What is the probability for a tall yellow offspring?
_______ What is the probability for a tall green offspring?
_______ What is the probability for a short yellow offspring?
_______ What is the probability for a short green offspring?
Co-Dominance and Multiple Alleles
There are four blood types: A, B, AB, and O. However there are three alleles that control
blood types:
IA, IB, and i. Alleles IA and IB are codominant, and the allele “i” is recessive.
1.
What are the two genotypes for type A blood?
What are the two genotypes for type B blood?
What is the one genotype for type AB blood?
What is the one genotype for type O blood?
2.
A man has type A blood and his wife has type B blood. A physician types the blood of their
four children and finds that each of the children has a different blood type. What are the
genotypes of the parents? How would you explain that all four blood types could be
represented by these four children?
3.
A couple preparing for marriage have their blood typed along with the other blood tests.
Both are AB. They ask what blood types their children may have. What would you tell
them?
Answers:
Monohybrid Question
1- Deafness in Cocker Spaniels is inherited. The allele for deafness is recessive to the allele for
normal hearing. Two cocker spaniels with normal hearing are mated together. They produce a
litter of eight pups, two of which are found to be deaf. (a) Give the genotypes of the parents. (b)
Show the possible genotypes, phenotypes and probabilities for the offspring. (c) How many of
the puppies will be unable to produce deaf offspring?
Answer:
Non Dominance or Incomplete Dominance
1-In four o’clocks, flower color is due to nondominance. Some flowers are red, some are white,
and others are pink. Cross a red flower with a pink flower.
a) What is the genotype of the red flower?
b) What is the genotype of the pink flower?
c) What is the probability of getting red offspring?
d) What is the probability of getting white offspring?
e) What is the probability of getting pink offspring?
Answer
Pedigree Charts
Queen Victoria was the world’s most famous carrier of hemophilia. Her son, Leopold, and
two carrier daughters, Alice and Beatrice, spread the allele fairly widely through the royal
families of Europe, Prussia and Russia. Fortunately, no modern monarchs have inherited
the allele. Indicate the probably genotype of each of the people below. Remember,
hemophilia is a sex-linked trait and shaded individuals have the disease.
Answer:
Sex Linked Traits
1- Brown eyes are dominant over blue eyes. This is NOT a sex-linked trait. Cross a brown-eyed
colorblind male (whose mother had blue eyes) with a normal blue-eyed female (whose
father was colorblind).
a) What is the genotype of the male?
b) What is the genotype of the female?
c) What is the probability of getting offspring that are blue-eyed carrier females?
(Remember that a carrier is a female that carries one copy of the sex-linked allele, but
does not have the disease.)
d) What is the probability of getting offspring that are blue-eyed?
e) What is the probability of getting offspring that are blue-eyed colorblind males?
f) What is the probability of getting offspring that are brown-eyed carrier females?
g) What is the probability of getting offspring that are blue-eyed normal males?
h) What is the probability of getting offspring that are colorblind?
Answer: