Download Genetics Problems: Monohybrid Crosses

Genetics Problems: Monohybrid Crosses
Answer the following questions in your binder. Be sure to define your alleles, show the
Punnett Square, and make some conclusions about the genotypes and phenotypes.
1. In peas, round seeds are dominant to wrinkled. Cross a hybrid round with a hybrid round.
2. In a certain type of plant, brown seeds are dominant to white seeds. Determine the
results of crossing a heterozygous brown seed with a white seed.
3. In peas, round is dominant to wrinkled, green is dominant to yellow, and tall plants are
dominant to short plants. Perform the following crosses:
a. hybrid green with a pure green
b. homozygous tall with a short plant
c. short plant with a short plant
4. The gene for brown color is dominant in cats to the gene for black color. Show a cross
between a pure brown cat and a pure black cat.
5. Usually, though not invariably, human eye color is inherited as if brown eyes were due to a
dominant factor and blue due to the corresponding recessive. Assume that this is correct
in this and the following problems. A man with blue eyes marries a brown eyed woman
whose mother has blue eyes. What proportion of the children would be expected to have
blue eyes?
6. A brown eyed man marries a blue eyed woman. The first child is blue eyed. What is the
man’s genotype? Show a cross to prove your answer.
7. Which is more likely: two brown eyed parents producing a blue eyed child or two blue
eyed parents producing a brown eyed child. Show crosses to support your answer.
8. If rough coated guinea pigs were crossed with smooth coated ones, and 25 offspring were
produced, all of which were rough coated, which was the dominant character? Why?
Show the cross which proves it. If these 25 guinea pigs of the F1 generation were
crossed with each other and produced 240 offspring, how many of the F2 generation
would you expect to have:
a. rough coats
b. pure rough coats
c. hybrid rough coats
d. smooth coats
e. hybrid smooth coats
9. In cattle, the polled (hornless) condition is due to a dominant gene while its recessive
allele causes horns to appear. Two polled cattle have a calf which develops horns as it
matures. Show the genotypes of all three. Prove your answer using a cross.
10. In squash, the allele for white fruits is dominant over the allele for yellow. If a whitefruited plant is crossed with a yellow-fruited plant and all the offspring are yellow, what
are the possible genotypes of the parents and the offspring?
11. In sheep, white is due to a dominant gene, black to its recessive allele. A white ewe
mated to a white ram produces a black lamb. If they produce another offspring, could it
be white? If so, what are the chances of it being white? List the genotypes of all the
animals mentioned in the problem.