Question 1

Which of the following best describes a 'haplosufficient' allele?

Accepted Answer

An allele where one copy is enough to produce a wild-type phenotype in heterozygotes.

Question 2

A cross between two pure-breeding white-flowered sweet peas produces all purple F1 offspring. When these F1 are selfed, the F2 generation shows a 9:7 ratio of purple to white flowers. What genetic phenomenon does this illustrate?

Accepted Answer

Complementary gene interaction

Question 3

Which of the following is an example of incomplete dominance?

Accepted Answer

A heterozygote displays a phenotype intermediate between both homozygotes.

Question 4

In the ABO blood group system, which genotype(s) will result in blood type AB?

Accepted Answer

$$I^A I^B$$

Question 5

A mutation that produces a protein with a new function not found in the wild type is called:

Accepted Answer

Neomorphic mutation

Question 6

A cross between two heterozygous yellow mice ($$A^Y A) $$produces a 2:1 ratio of yellow to agouti offspring. What is the most likely explanation for the missing class?

Accepted Answer

The $$A^Y$$ allele is a dominant lethal when homozygous.

Question 7

Which of the following best describes variable expressivity?

Accepted Answer

A genotype produces a range of phenotypes with varying severity.

Question 8

In a dihybrid cross showing dominant epistasis, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$12:3:1$$

Question 9

A patient with phenylketonuria (PKU) can avoid symptoms by adhering to a special diet. This is an example of:

Accepted Answer

Gene–environment interaction

Question 10

Which of the following is true about codominance?

Accepted Answer

Both alleles are expressed in the heterozygote, resulting in a phenotype distinct from either homozygote.

Question 11

A gene mutation that produces no functional gene product is called:

Accepted Answer

Null (amorphic) mutation

Question 12

Which of the following best describes pleiotropy?

Accepted Answer

A single gene affects multiple distinct traits.

Question 13

In a complementation test, two pure-breeding mutants are crossed and the F1 offspring all display the wild-type phenotype. What does this indicate?

Accepted Answer

The mutations are in different genes.

Question 14

Which of the following is an example of a sex-influenced trait?

Accepted Answer

Beard development in goats, where $$B_1B_2$$ males are bearded but $$B_1B_2$$ females are beardless.

Question 15

A dihybrid cross between $$AaBb$$ individuals produces a 9:3:4 phenotypic ratio in the F2 generation. What type of gene interaction is this?

Accepted Answer

Recessive epistasis

Question 16

Which of the following best explains why Huntington disease persists in human populations despite being a dominant lethal allele?

Accepted Answer

It has a delayed age of onset, allowing affected individuals to reproduce before symptoms appear.

Question 17

Which of the following is true about the allelic series of the C gene in mammals?

Accepted Answer

The C allele is dominant over all other alleles in the series.

Question 18

A trait is said to have incomplete penetrance when:

Accepted Answer

Not all individuals with the genotype express the expected phenotype.

Question 19

Which of the following best describes dominant negative mutations?

Accepted Answer

A mutant allele whose product interferes with the function of the wild-type protein in multimeric complexes.

Question 20

In a dihybrid cross showing duplicate gene action, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$15:1$$

Gene Interaction and Allelic Relationships: Structured Study Notes for Genetics Students

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