Question 1

Which of the following best describes incomplete dominance, as seen in the cross between red and white snapdragon flowers?

Accepted Answer

The heterozygote expresses a phenotype intermediate between the two homozygotes.

Question 2

A cross between two yellow mice (genotype $$A^Y A) $$produces offspring in a 2:1 ratio of yellow to agouti. What is the genetic explanation for this result?

Accepted Answer

Yellow is a dominant lethal allele, so $$A^Y A^Y$$ individuals die.

Question 3

Which of the following is an example of codominance?

Accepted Answer

ABO blood types, where both $$I^A$$ and $$I^B$$ alleles are expressed in the AB phenotype.

Question 4

A woman with genotype $$I^A I^B$$ and $$Hh$$ for the FUT1 gene has children with a man who is $$I^B I^B$$ and $$Hh. $$What is the probability that their child will have blood type O?

Accepted Answer

$$1/16$$

Question 5

Which of the following best describes epistasis?

Accepted Answer

One gene masks or modifies the expression of another gene at a different locus.

Question 6

In a dihybrid cross involving recessive epistasis (such as coat color in mice), what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:4$$

Question 7

Which of the following statements about the Bombay phenotype is correct?

Accepted Answer

Individuals with genotype $$hh$$ cannot express A or B antigens, regardless of their ABO genotype.

Question 8

A cross between two pure-breeding white-eyed Drosophila produces all red-eyed offspring. When these F1 are crossed, some F2 have white eyes. What does this indicate?

Accepted Answer

The white eye phenotype is caused by mutations in different genes (complementation).

Question 9

Which of the following is an example of pleiotropy?

Accepted Answer

Marfan syndrome, where a single gene affects connective tissue, eye lens, and aorta.

Question 10

Which of the following best describes sex-limited inheritance?

Accepted Answer

A trait is expressed in only one sex, even though both sexes carry the gene.

Question 11

A man with hemophilia (an X-linked recessive disorder) and a woman who is a carrier have a child. What is the probability that their son will have hemophilia?

Accepted Answer

$$0.5$$

Question 12

Which of the following best explains why calico cats are almost always female?

Accepted Answer

The gene for coat color is X-linked, and X-inactivation in females leads to patchy coloration.

Question 13

Which of the following is an example of a gene-environment interaction?

Accepted Answer

A gene for pigment production is only expressed at certain temperatures.

Question 14

Which of the following best describes penetrance?

Accepted Answer

The proportion of individuals with a given genotype who express the associated phenotype.

Question 15

In a population, a gene has 10 different alleles. How many different genotypes are possible at this locus?

Accepted Answer

$$\frac{n(n+1)}{2} = \frac{10 	imes 11}{2} = 55$$

Question 16

Which of the following is true about dominant lethal alleles?

Accepted Answer

They can persist in a population if they have a late onset, as in Huntington's disease.

Question 17

A cross between two heterozygotes for two genes (AaBb x AaBb) produces a 9:7 phenotypic ratio. What is the most likely explanation?

Accepted Answer

Complementary gene interaction, where both dominant alleles are required for the phenotype.

Question 18

Which of the following is an example of a position effect?

Accepted Answer

A gene's expression is altered because it is relocated near heterochromatin.

Question 19

Which of the following best describes expressivity?

Accepted Answer

The degree or range to which a phenotype is expressed among individuals with the same genotype.

Exceptions to Mendelian Genetics: Extensions and Non-Mendelian Inheritance

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