Genetics Problems Packet
Complete each of the problems on a separate piece of paper. Be sure to include:
A. a key showing the genotypes and phenotypes
B. write the parents cross in words
C. write the parents genotype
D. punnett square
E. genotypic ratio
F. phenotypic ratio
G. Answer any other questions that are asked relating to the problem.
*Keep in mind that some problems may require more than one cross!!!*
Monohybrid Problems:
1. Cross a heterozygous pea plant, which bears its flowers axially with a
homozygous pea plant, which bears its flowers terminally.
2. Cross a heterozygous pea plant with smooth pods with a homozygous
constricted pod plant.
3. Cross a homozygous yellow-seeded pea plant with a homozygous green-seeded
pea plant.
4. Short hair is dominant over long hair in guinea pigs. Cross a homozygous shorthaired female guinea pig with a long-haired male. If their offspring were to mate
and produce an F2 generation, what genotypic and phenotypic offspring will
result and in what ratio.
5. Two brown mice were mated and twelve offspring resulted. Nine of the offspring
were brown, and three were white. How can this be explained?
6. Starchy grain is dominant over sugary grain in corn. If a cross between these two
types of corn was performed and 58 of the offspring were sugary, how many
would you expect to be starchy?
7. Use your imagination. A pink circus elephant and a green circus elephant were
mated and only pink baby elephants were born. If two of these offspring were
mated and eventually produced a total of 64 baby elephants, how many of these
should be pink and how many should be green?
8. Short hair is dominant over long hair in guinea pigs. A short-haired guinea pig
(one of its parents had long hair) was mated with a long-haired guinea pig. If
blindfolded, you selected one of the guinea pigs from the cage, what is the
chance that you would get a long-haired animal?
9. Brown color in mice is dominant over albinism. In a cross between a brown
mouse and an albino mouse, six of the offspring were brown and five were
albinos. Show how this is possible.
10. Two parents with cleft chins have a child with a smooth chin. Show how this can
happen.
11. The trait for big ears is dominant in elephants. A big-eared elephant marries a
small-eared elephant. All of their children have big ears. If two of the children
mate and produce offspring, what are the phenotypic and genotypic ratios of the
grandchildren?
Incomplete Dominance Problems:
1. If a red Japanese four-o’clock flower is crossed with a white one, all the offspring
will be pink. Perform each of the crosses below.
A. white plant crossed with a pink plant
B. red plant crossed with a pink plant
C. two pink plants are crossed
D. two red plants are crossed
2. In some cats the gene for tail length shows incomplete dominance. Cats with
long tails and those with no tails are homozygous for the respective alleles. Cats
with one long-tail allele and one no-tail allele have short tails. Perform the
crosses below:
A. a long tail cat and a cat with no tail
B. a long tail cat and a short tail cat
C. a short tail cat and a cat with no tail
D. two short tail cats
3. Fruit color in summer squash can be white, yellow, or green. A parental cross of
true breeding white and yellow fruit varieties result in all green fruits, if two green
fruit plants are mated, what are the possible offspring?
4. Mating between palomino horses yields an overall phenotypic ratio among their
offspring of 1 chestnut: 2 palomino: 1 cremello. Predict the outcome of the
following crosses:
A. palomino X chestnut
B. palomino X cremello
C. cremello X cremello
5. Two short tailed (Manx cats) are bred and produce three kittens with long tails,
five kittens with short tails and one kitten with no tail. Show how this is possible.
Codominance Problems:
1. In short horned cattle, coat color is codominant. A heterozygous individual will
have a coat color with a mixture of red and white hairs, called roan. If a white cow
is crossed with a roan bull, what types of offspring are expected?
2. What would result from the cross of 2 roan cattle?
3. The blue Andalusian variety of chickens has slate blue feathers, which are really
speckled black and white. This variety is produced when birds with white feathers
are mated with birds with black feathers. A farmer wants all black chickens. He
has two blue chickens to begin with. Show how he could develop a pure black
breeding chicken farm.
4. Use your imagination…a pink circus elephant finds a purple circus elephant to
marry. Imagine the ringmaster’s surprise when he sees two babies, pink and
purple spotted elephants. Show the genotypes of the parents and the children.
The spotted elephants are a big hit and the ringmaster thinks he can mate the
two spotted elephants to make a family of spotted elephants. Show genetically if
this possible or is he nuts.
5. Red blood cells that are crescent shaped are called sickle cells and are present
in individuals with sickle cell anemia. Individuals who are homozygous for sickle
cell produce only sickle shaped cells and have severe anemia. Individuals who
are heterozygous produce both normal and sickle shaped cells and have a mild
case of anemia. What are the chances of a couple that both suffer from the mild
form of sickle cell anemia to have normal children?
Sex-Linked Problems:
1. A woman, who is heterozygous for hemophilia, marries a normal man. Show the
cross.
2. A woman who is a carrier for hemophilia marries a hemophiliac man. Show the
cross.
3. A phenotypically normal woman has phenotypically normal parents. However,
she has a hemophiliac brother.
A. What are her chances of being a carrier for hemophilia?
B. If she is a carrier and marries a normal male, what is the chance of a child
being a hemophiliac?
4. If a normal sighted woman whose father was color-blind marries a color-blind
man, what is the probability that they will have a son who is color-blind? What is
the probability that they will have color-blind child?
5. In fruit flies, white eyes are a sex-linked recessive trait. Normal eye color is red. If
a white-eyed make is crossed with a heterozygous female, what proportion of the
offspring will have red eyes?
6. A man who suffers from a sex-linked disorder called “Flippites” (constant
changing of the channels) marries a woman who likes to watch one program at a
time. They have 6 children, 3 girls and 3 boys. Two of the boys suffer from
Flippites and one of the girls does. How could this be?
Dihybrid Problems:
For problems 1-4: Some mice run in circles (waltzing mice), a recessive gene causes
this. Mice with the normal gene are called running mice. Black fur is dominant to brown
fur.
1. Cross a heterozygous running, heterozygous black mouse with a homozygous
running, homozygous black mouse.
2. Cross a homozygous running, homozygous black mouse with a heterozygous
running, brown mouse.
3. Cross a waltzing brown mouse with a waltzing brown mouse.
4. Cross a heterozygous running, heterozygous black mouse with a heterozygous
running, heterozygous black mouse.
5. Cross a plant that is heterozygous for green pods and for being tall with a plant
that has yellow pods and is also heterozygous tall.
Blood Type Problems:
1. A woman homozygous for type B blood marries a man who is heterozygous type
A. what blood types are expected in their children?
2. A man with type O blood marries a woman with type AB blood. What blood types
are expected in their children?
3. A type B woman whose mother was type O marries a type O man. What blood
types are expected in their children?
4. A type A woman whose father was type B marries a type B man whose mother
was type A. What blood types are expected in their children?
5. What is the probability that a couple whose blood types are AB and O will have a
type A child?
6. A couple has a child with type A blood. If one parent is type O, what are the
possible genotypes of the other parent?
Mixed Problems:
Complete the problems below as instructed on the first page, but also include the type
of cross. Choose from normal, incomplete dominance, codominance, sex-linked
inheritance, blood types, and dihybrid crosses.
1. A homozygous recessive black-bodied female fruit fly is crossed with a
heterozygous tan male.
2. A homozygous recessive black-bodied female fruit fly that is homozygous
dominant for straight wings is crossed with a heterozygous tan-bodied male fruit
fly that is heterozygous for straight wings.
3. A woman with type AB blood marries a man with type O blood. What are the
possible blood types of their children?
4. A pink flower is crossed with a white flower. What color will the offspring be? Red
is incompletely dominant to white, therefore a heterozygous individual will be
pink.
5. A woman has type AB blood her child is type A. She isn’t sure who the father is.
There are 4 possible fathers, each with a different blood type. Which father is the
real one or who can be ruled out?
Bachelor #1 type A
Bachelor #3 type AB
Bachelor #2 type B
Bachelor #4 type O
6. A homozygous recessive short, pink flowered plant is crossed with a
heterozygous tall, purple plant. What are the genotypes and phenotypes of the
offspring.
7. Two parents with cleft chins have a child with a smooth chin. How is this
possible?
8. A person with free ears marries another person with attached ears. They have 12
children, some of which have attached ears. What are the genotypes of the
parents? How many children will have attached ears? Which trait is dominant?
9. “Not wanting to stop and ask for directions” is a sex-linked recessive disorder. If a
normal female (XAXA) has children with a male (XaY) who never stops to ask
directions, what percentage of their children will have the disorder?
10. A couple had eight children, four boys and four girls. Two boys have a genetic
disorder “Burpitis”. The parents are normal. Show how this is possible.
11. A blue pig and pink pig have children. The children are pink and blue spotted.
Show how this is possible.
12. Two green dogs have puppies. The puppies are either blue, green, or yellow.
Show how this is possible.
13. A couple, both with blood type AB claim that the hospital where their child was
born, switched their baby with another. The child they brought home is type O.
Can you prove their case?
14. A round head martian has children with a square head martian. Half of the
children martians have a round head, and half square. If one round head child
martian mates with one square head child, what are the genotypic and
phenotypic ratios of the grandchildren martians?
15. A big butt elephant with long eyelashes has children with a small butt elephant
with short eyelashes. All of the children have big butts and long eyelashes. If two
children mate, what ratios are expected in the grandchildren?
16. A purple frog and a green frog have children. The children are green and purple
striped. Show how this is possible.
17. A couple had four children, two boys and two girls. Both boys have a genetic
disorder “Fear of Commitment Syndrome”. The parents are normal. How could
this happen?
18. Glaucoma is a dominant trait, G, normal eyes is gg. Having cataracts is
recessive, rr, not having cataracts is R (normal). If a person who is heterozygous
for both traits marries another person who is heterozygous for glaucoma, but
normal for cataracts, what is the probability of the offspring having both problems
in their eyes?
19. Mrs. Curly-Q is heterozygous for curly hair. She marries Mr. Poker-Straight, who
is homozygous recessive for straight hair. They want to know what chance there
is that one of their children has curly hair.
20. The same Mrs. Curly-Q as above is also heterozygous for brown hair. Mr. PokerStraight has blonde hair. They now want to know what chance there is that one
of their children will have blonde hair.
21. You have a female guinea pig named Fluffy. Fluffy is heterozygous for long hair
and black hair. Your friend’s guinea pig, Snowball, is heterozygous for long hair,
but has white hair. What types of offspring can you expect?