Genetics Quiz 3

The diagram shows the X chromosomes in a female fruit fly and the X and Y chromosomes in a male fruit fly. 

The two fruit flies are crossed with each other. The female offspring of the fruit flies will receive which pair of chromosomes?

• A

• B

• C

• D

Answer explanation

The female offspring will inherit one X chromosome from the mother and one X chromosome from the father. Therefore, they will receive the pair of chromosomes represented in choice A, which shows two X chromosomes.

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A pea plant with homozygous genes for round seeds is crossed with a pea plant that is homozygous for wrinkled seeds.

Which statement correctly predicts the results of the genetic cross?

• All the offspring will have the genotype RR.

• All the offspring will have the genotype Rr.

• Half the offspring will have the genotype RR and half will have rr.

• All the offspring will have the genotype rr.

• Half the offspring will have the genotype Rr, one quarter will be RR and one quarter will be rr.

Answer explanation

The round seed trait (R) is dominant over the wrinkled seed trait (r). Crossing a homozygous round (RR) with a homozygous wrinkled (rr) results in all offspring having the genotype Rr, displaying round seeds.

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If Jessica has blue eyes (bb) and both of her parents have brown eyes (Bb), which of the following statements is true?

• Jessica inherited one recessive form of the gene from each parent.

• Jessica inherited both genes from her mother.

• Jessica inherited one dominant form of the gene from each parent.

• Jessica inherited both genes from her father.

Answer explanation

Jessica has blue eyes (bb), meaning she must have inherited a recessive gene (b) from both parents. Since both parents are Bb, they can pass on either a dominant (B) or recessive (b) gene, confirming she got one recessive from each.

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Which statement best describes the pattern of inheritance that produces 100% red-flowered offspring when a red flower is crossed with a white flower?

• Both red flowers and white flowers are dominant.

• Both red flowers and white flowers are recessive.

• Red flowers are dominant and white flowers are recessive.

• Red flowers are recessive and white flowers are dominant.

Answer explanation

The correct choice is that red flowers are dominant and white flowers are recessive. This explains why crossing a red flower with a white flower results in 100% red-flowered offspring, as the dominant trait masks the recessive one.

In guinea pigs, being hairless is a recessive trait. If two heterozygous hairy guinea pigs reproduce, what are the chances that they will have a hairless offspring?

• 0%

• 25%

• 50%

• 75%

• 100%

Answer explanation

In a cross between two heterozygous hairy guinea pigs (Hh x Hh), the possible genotypes are HH, Hh, Hh, and hh. Only the hh genotype results in hairless offspring, which is 1 out of 4, or 25%.

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Hawaiian happy face spiders from the island of Maui can have different markings, as shown below. A single gene determines the marking on the spiders. A plain spider is crossed with a patterned spider. The patterned spider is homozygous. The pattern allele is dominant.

What percentage of the offspring from this cross are expected to be patterned instead of plain?

• 0%

• 25%

• 50%

• 75%

• 100%

Answer explanation

The plain spider is homozygous recessive (pp) and the patterned spider is homozygous dominant (PP). All offspring (Pp) will inherit the dominant pattern allele, resulting in 100% patterned spiders.

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A partial Punnett square is shown. Which of the following statements describes the parental genotypes that would result in this Punnett square?

• Both parents are heterozygous.

• Both parents are homozygous dominant.

• Both parents are homozygous recessive.

• One parent is homozygous dominant and the other parent is heterozygous.

• One parent is homozygous recessive and the other parent is heterozygous.

Answer explanation

The Punnett square indicates a mix of dominant and recessive alleles. One parent being homozygous dominant (AA) and the other heterozygous (Aa) would produce offspring with both dominant and recessive traits, matching the square.

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Height is a polygenic trait in humans. Which of the following statements best explains the genetics of this trait?

• The gene for height is located on the Y chromosome.

• The gene for height is located on the X chromosome.

• Height is controlled by a single dominant gene.

• Height is controlled by more than one gene.

Answer explanation

Height is a polygenic trait, meaning it is influenced by multiple genes rather than a single gene. This complexity allows for a range of heights in the population, making the statement that height is controlled by more than one gene the best explanation.

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Humans may have type O, A, B, or AB blood. This blood trait is determined by: 

• genes on X chromosomes only.

• a double crossover on the X chromosome.

• multiple alleles.

• three homologous chromosomes.

Answer explanation

The blood types O, A, B, and AB are determined by multiple alleles (IA, IB, i) at a single gene locus, allowing for various combinations that result in different blood types.

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In the winter, the fur of the arctic fox is white. In the summer, the fur darkens to a reddish brown. What most likely causes the fur of the fox to change color?

• the fox's age

• amount of sunlight present

• the fox's habitat

• the fox's genes

Answer explanation

The color change in the arctic fox's fur is primarily controlled by its genes, which dictate the seasonal adaptations for camouflage. This genetic mechanism allows the fur to change from white in winter to reddish brown in summer.

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