Download GENETICS EXERCISES

GENETICS EXERCISES
DIRECTIONS: Read each problem below carefully and follow these steps: 1) Determine
the pattern of inheritance (complete dominance, incomplete dominance, sex-linked, multiple
alleles, codominance, polygenic inheritance), 2) Write the cross correctly, 3) Work the
problem using a punnett square, 4) Interpret your results, 5) Answer the specific
question(s). Show all work and circle all answers. Work carefully and double-check ALL
questions.
1) Brown eyes are dominant and blue eyes are recessive. A woman with brown eyes
marries a man with blue eyes.
A) What is the probability that their children will have blue eyes if the woman is
heterozygous?
B) What is the probability that their children will have blue eyes if the woman is
homozygous?
2) Short hair is dominant in rabbits, while long hair is recessive. A short-haired rabbit’s
offspring has long hair. What was the genotype of the short-haired rabbit? ____
Prove your answer with a punnett square.
3) In humans, a hitchhiker’s thumb is recessive to a normal thumb. Suppose a man with a
hitchhiker’s thumb marries a woman with a normal thumb whose father had a
hitchhiker’s thumb. What fraction of their children, would you predict, will have a
hitchhiker’s thumb?
4) If a litter of cats resulting from the mating of two short-tailed cats contains three
kittens without tails, two with long tails, and six with short tails, what would be the type
of inheritance exhibited by tail length in these cats?
5) In snapdragons, crossing a red and a white snapdragon results in all pink snapdragons.
What will be the results of a cross between two pink-colored snapdragons? Give the
answer in a phenotypic ratio.
6) A man is heterozygous for blood type B, while his fiancee is heterozygous for blood type
A. They plan to marry and have several children.
A) What is the possible genotypic ratio of their offspring?
B) What is the possible phenotypic ratio of their offspring?
7) In humans, assume that brown eyes (B) are dominant over blue eyes (b) and righthandedness (L) is dominant over left-handedness (l). A brown-eyed, right-handed man
marries a blue-eyed, right-handed woman and their first child is blue-eyed and lefthanded. What are the genotypes of the two parents? Prove your answer in a punnett
square.
Mother =
Father =
8) Hemophilia is a sex-linked trait and is recessive (h). The normal condition for blood
clotting is dominant. A man with hemophilia marries a woman who neither has hemophilia
nor is a carrier of the disease.
A) What are the possible gametes produced by the mother and the father?
Mother’s gametes =
Father’s gametes =
B) What fraction of their sons will have hemophilia?
C) What fraction of their daughters will carry hemophilia?
D) Which parent, the mother or the father, gives a son his genetic information on the
23rd chromosome?
9) Some dogs bark while trailing and others are silent. The barking trait is due to a
dominant allele. Erect ears are dominant to drooping ears.
A) What type(s) of puppies could be expected from a male heterozygous erect-eared,
heterozygous barker mated to a female with identical genetic information?
B) List all possible gametes produced by the male dog. ______________________
C) List all possible gametes produced by the female dog. ____________________
10) A man with type AB blood marries a woman with type A blood and their first child has
type O blood.
A) Does the man have reason to believe the daughter is not his biological child?
B) Prove your answer to “A” with a punnett square(s).
11) A homozygous black chicken is crossed with a homozygous white chicken and the result
is black and white checkered chickens.
A) What is the pattern of inheritance for feather color in these chickens? ________
B) What would be the phenotypic ratio of offspring if a heterozygous black and white
chicken is crossed with a another heterozygous black and white chicken?
12) A man has reason to believe that the hospital may have accidently “switched” babies
when his daughter was born. He requests a blood test be performed. His blood type is
A, his wife is B, and their daughter is A. The other set of parents have the following
blood types: father= AB, mother = B, baby = AB. Were the babies “switched”? Prove
your answer with two punnett squares.
13) A man and his wife both have normal vision, but their son is colorblind. Which parent,
the mother or the father gave the son the colorblind allele? ________ Prove your
answer in a punnett square.