Genetics Problems
Name: ____________________________________________________________ Date: ___________________ Block: _______
7.1 Single Trait Genetics Problems
1. In gerbils, black hair is dominant over white hair. Two heterozygous parents are crossed.
a. What are the alleles for this gene? What letters will you use to define each allele?
b. What are the genotypes & phenotypes of the parents?
c. What are possible genotypes of the F1? What is the genotypic
ratio?
d. What are the possible phenotypes of the F1? What is the phenotypic ratio?
2. For cats, the allele for long hair is dominant over the allele for short hair. A heterozygous female is
crossed with a short hair male.
a. What are the alleles for this gene?
b. What are the genotypes of the parents?
c. What are the genotypes and phenotypes of the offspring?
d. This cross yielded 20 kittens. How many would you expect to be short haired?
Genetics Problems
3. In petunias yellow flowers are dominant over white flowers. Cross a homozygous yellow petunia
with a white petunia.
a. What are the alleles for this gene?
b. What are the genotypes of the parents?
c. What are the genotypes and phenotypes of the offspring?
4. Attached ear lobes is dominant over nonattached ear lobes. A man heterozygous for ear lobe type
marries a woman homozygous dominant for ear lobes. Give the genotypes and phenotypes of
their children in the correct ratios.
5. In bees, striped bodies is dominant over no stripes. Two striped bees mated and produced striped
bees AND non-striped bees. What are the genotypes of the parents? Use a punnett square to
prove your conclusion.
Genetics Problems
7.2 Dominance & Blood Type Problems
6. Raccoons have dark rings around their tails. If a raccoon with wide bands around its tail mates
with a raccoon with narrow-width bands around its tail, they produce offspring with mediumwidth bands around their tails.
a. What type of dominance is this? ___________________________________________
b. What are expected genotypes and phenotypes of the offspring resulting from a cross
between a narrow-width band raccoon and a medium-width band raccoon?
7. In squirrels, hair length shows incomplete dominance; long haired squirrels and short haired
squirrels mate to produce medium-length hair squirrels.
a. A medium-length haired squirrel mates with a long haired squirrel. What fraction of
their offspring will have medium length hair?
b. What crosses (combinations of parents) could produce a short-haired squirrel?
8. In petunias a light purple flower is produced when a white and dark purple flower are crossed. If
a light purple flower is crossed with a dark purple flower:
What type of dominance is this? ______________________
Write the cross: ___________________________
The genotypes of the offspring:
The phenotypes of the offspring:
The phenotypic ratio: ________________________
Genetics Problems
9. In cows, a red and white cow (called “roan”) is produced when a red cow mates with a white bull.
a. Predict the phenotypic ratios of offspring when a white cow is crossed with a roan bull
b. A farmer only wants to breed cattle with red fur – what should the genotypes &
phenotypes of the parents be? Verify your results with a punnett square.
10. A cross between a black cat and a tan cat produces a tabby patterns (black & tan fur).
a. What type of dominance is this? _____________________________________
b. What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?
11. In a certain breed of flower, blue and white colored petals are codominant with each other;
heterozygotes show both colors on their flowers. Two heterozygotes are crossed:
Parental genotypes: ________________________________________
Genotypes of offspring:
Genotypic ratio:
Phenotypes of offspring:
Phenotypic ratio:
Genetics Problems
12. Mom has type O blood. Dad has type AB blood. What percentage of their kids will inherit type B
blood?
13. A woman sues a man for child support, claiming he is the father of her illegitimate child. The
woman is type A blood, the man is type B blood, and the child is type O blood. Show how it is
possible for this man to be the father of this child.
14. A wealthy elderly couple dies together in an accident. A man comes forward, claiming that he is
their long lost son and is entitled to their fortune. The couple were of blood types AB and O. The
man has type O blood. Could he be the heir to the fortune? Show why or why not.
15. John has type O blood. He knows his mother had type B blood. He does not know the identity of
his father, however. What possible blood types could his father have had? Show your work.
Genetics Problems
7.3 Sex-linked Genetics Problems
Sometimes a gene for a trait is carried on the X chromosome. This makes the inheritance patterns
different for male and female offspring as males have an XY genotype and females an XX. If the trait is
recessive, a female will need both X’s to have the gene to show the trait while a male will always show the
trait for the gene on his X. Such a trait is called sex-linked.
16. White eyes in fruit flies is a sex-linked recessive trait. Using a E for the dominant red-eye allele and
an e for the recessive white eyed allele for the trait of eye color: A white eyed male’s genotype is
XeY and a red eyed male’s genotype is XEY. A red eyed female’s genotype is: XEXE or XEXe and a
white eyed female’s is XeXe .
Cross a white eyed male with a heterozygous red eyed female. What are the possible eye colors for
their male and female offspring?
17. Colorblindness in humans is a sex-linked recessive trait. Could a colorblind man have all normal
children with a normal woman with no history of colorblindness in her family? What about if her
father was colorblind?
Genetics Problems
18. Hemophilia is a sex-linked recessive trait. If a woman who has a hemophiliac father married a
normal man what are the chance of their son or daughters being hemophiliacs?
19. Colorblindness is a recessive sex-linked trait (carried on the X chromosome). A normal man marries a
colorblind woman.
Parental genotypes :____________________________________________________________
a. What is the probability that their male children will have normal vision?
b. What is the probability that their female children will have normal vision?
Genetics Problems
7.4 Two-trait Crosses
20. Complete the Punnett Square below showing a dihybrid cross between tomato plants with purple
stems and red fruit.
Parent 1 Genotype: ______________
Parent 2 Genotype: ______________
Parent 1 Possible Gametes: ____________________
Parent 2 Possible Gametes: __________________
Key:
P = purple stem
p = green stem
R = red fruit
r = yellow fruit
The expected phenotypic ratio for this cross is 9:3:3:1. Next to each of these numbers, write a
description of the phenotype it represents. One is done for you.
9: ________________________________________________________________________________
3: _________________________________________________________________________________
3: green stem, red fruit
1: __________________________________________________________________________________
21. A tall green pea plant (TTGG) is crossed with a short white pea plant (ttgg). Use the Punnett square below
to answer the following questions.
TT or Tt = tall
a.
tt = short
GG or Gg = green
gg = white
What is the phenotype of all the offspring?
____________________________________________________
b. What is the genotype of all the offspring?
____________________________________________________
c. How many offspring are homozygous dominant for
the traits? _____________________________________
d. How many offspring are homozygous recessive for
the traits? _____________________________________
TG
TG
TG
TG
tg
TtGg
TtGg
TtGg
TtGg
tg
TtGg
TtGg
TtGg
TtGg
tg
TtGg
TtGg
TtGg
TtGg
tg
TtGg
TtGg
TtGg
TtGg
e. How many offspring are heterozygous for the traits? ____________________________________________
Genetics Problems
22. Use the cross below to answer the following questions.
a. What is the genotype for the square that is colored in? __________________________________________
b. What is the phenotype of the square that is colored in? __________________________________________
c. What would be the genotype for an offspring that is rough and yellow? _____________________________
d. What would be the phenotype for an offspring that is AaBb? _____________________________________
e. What fraction of the offspring will be rough and green? Remember to express this as #/16.
____________
f.
What fraction of the offspring will be AAbb? __________________________________________________
g. What fraction of the offspring will be homozygous dominant for both traits? ________________________
h. What fraction of the offspring will be heterozygous for both traits? ________________________________
23. A woman with the genotype PpRr is crossed with a man with the genotype PPRr. Use the punnett square
for this dihybrid cross below to answer the questions below.
a. What is the genotype of the mom?
_______________________________________________
b. What is the phenotype of the father?
_______________________________________________
c. What fraction of the offspring will be
PPRR?
_______________________________________________
d. What fraction of the offspring will have
Puffy, red lips?
_________________________________________
e. What fraction of the offspring will be heterozygous for both traits? ________________________________
f.
Which of the four traits does not show up in any of the offspring? _________________________________