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 short-haired 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. Poker-Straight 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?