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Biology MCAS Monohybrid Cross Problems
1. Which of the following normally results from meiosis in a human cell that contains 46 chromosomes?
A. an egg cell with 46 chromosomes
B. a liver cell with 23 chromosomes
C. a blood cell with 46 chromosomes
D. a sperm cell with 23 chromosomes
Explain:
2. In humans, freckles are encoded by a dominant allele. An individual woman is heterozygous for freckles. According to
the law of segregation, which of the following would apply to a child of this woman?
A. The child must inherit the dominant allele for freckles.
B. The child must inherit the recessive allele for freckles.
C. The child has an equal chance of inheriting the dominant allele or the recessive allele for freckles from her
mother.
D. The child has a greater chance of inheriting the dominant allele than the recessive allele for freckles from her
mother.
Explain your answer using the terms chromosomes and meiosis.
3. Hawaiian happy face spiders from the island of Maui can have different markings, as shown below. A single gene
determines the markings on the spiders.
Plain Spider
Patterned Spider
A plain spider is crossed with a patterned spider. The patterned spider is homozygous. The pattern allele is dominant to
the plain allele. What percentage of the offspring from this cross are expected to be patterned instead of plain? Show the
Punnett square.
4. In cats, the allele for short hair (H) is dominant to the allele for long hair (h). If a heterozygous short-hair cat is crossed
with a long-hair cat, what percentage of the offspring is expected to be heterozygous for hair length? Show the Punnett
square.
5. In mussels, brown (B) coloring is dominant, and blue (b) coloring is recessive. If a blue mussel has two brown parents,
what percentage of the total offspring of these brown parents are expected to be blue? Show the Punnett square(s).
6. The illustration below shows two adult rabbits and their offspring.
In rabbits, the allele for spots (R) is dominant to the allele for solid color (r). What is the most likely genotypes of the
parent rabbits in the illustration? Show the Punnett square(s).
A.
rr x rr
B.
Rr x rr
C.
Rr x Rr
D.
RR x rr
7. In Suffolk sheep, the allele for white wool (W) is dominant, and the allele for black wool (w) is recessive. A farmer has
mated two sheep for a few years. These matings have resulted in six offspring, 4 with white wool and 2 with black wool.
One parent has white wool and the other has black wool. Which of the following could be the genotypes of the parent
sheep? Show the Punnett square(s).
a. WW and ww
b. WW and Ww
c.
Ww and ww
d. Ww and Ww