Biology 100 – Genetics Homework.
Due Date: See schedule and write here!
Instructions: Complete the following problems on lineless paper. Make sure you
show your work. Do not simply write down your answers. If you only write your answers you will not
receive full credit. Please number and letter your responses clearly. Also, clearly indicate the letter
symbols that you are using for each trait. Please highlight your final answer. Write legibly because if I
cannot read your work I cannot grade it.
1. In humans, PKU is an inherited metabolic disease, which if untreated, leads to death at about the age of
six. IT is inherited as a recessive trait. What is the probability that two heterozygous parents will have a
A) a PKU child? B) a heterozygous child? C) a homozygous non-PKU child?
2. Unattached earlobes are inherited as a dominant trait; attached earlobes a recessive trait. Suppose a
homozygous man with unattached earlobes marries a homozygous woman who has attached earlobes.
A) What type of earlobes will their children have? B) If these children marry someone with the same
genotype as themselves, will all of their children have attached lobes? Explain your answer.
For questions 3 & 4 below: Use this information – In horses, a black coat (B) is dominant to brown coat
(b) and being a trotter (T) is dominant to being a pacer (t).
3. A black pacer is crossed with a brown trotter. The offspring is a brown pacer. Give the genotype of all
of these horses.
4. A black pacer mater to a brown trotter produces a black trotter offspring. Give all possible genotypes
for this offspring.
5. If a child’s blood type is A and the mother’s blood type is O, what blood types might the father have?
What are the possible genotypes of the father?
6. A white guinea pig, whose parents were black, is crossed with a black guinea pig whose male parent
was white and whose female parent was black. Two white offspring result. Determine the genotypes of all
individuals mentioned. About which individual is there some doubt?
7. Both Mrs. Smith and Mrs. Jones had baby girls the same day in the same hospital. Mrs. Smith took home
a baby girl, whom she called Shirley. Mrs. Jones took home a baby girl named Jane. Mrs. Jones began to
suspect however that her child and the Smith baby had been accidentally switched in the nursery. Blood
tests were made. Mr. Smith is Type A, Mrs. Smith is Type B, Mr. Jones is Type A, Mrs. Jones is type A,
Shirley is Type O and Jane is Type B. Had a mix up possibly occurred?
8. If a family has two girls and are expecting a child, what is the chance it will be a boy?
9. A woman with normal color vision, whose father was color-blind, marries a man with normal vision.
What proportion of their A) sons is expected to be color-blind? B) daughters will be color blind? C)
daughters will be carriers of color-blindness.
10. Short hair is due to a dominant gene in rabbits and long hair to its recessive allele. A cross between a
short-haired female and a long-haired male produced a litter of one long-haired and seven short-haired
bunnies. A) What are the genotypes of the parents? B) What phenotypic ratio was expected in the
offspring generation? C) How many of the 8 bunnies were expected to be long-haired?