Question 1

Which statement best describes the 'one gene-one enzyme' hypothesis proposed by Beadle and Tatum?

Accepted Answer

Each gene encodes a single enzyme that catalyzes a specific step in a biochemical pathway.

Question 2

In a biosynthetic pathway for methionine synthesis, a mutant strain can only grow on minimal media supplemented with homocysteine or methionine. Which compound is the mutant most likely unable to convert?

Accepted Answer

Homocysteine

Question 3

A prototroph is defined as:

Accepted Answer

A strain that can synthesize all compounds required for growth.

Question 4

You perform a complementation test between two true-breeding mutants with the same phenotype. The F1 progeny all show the wild-type phenotype. What does this indicate?

Accepted Answer

The mutations are in different genes.

Question 5

In a genetic dissection experiment, four mutants are tested for growth on minimal media supplemented with different intermediates. Mutant 2 grows only on media supplemented with cystathionine, homocysteine, or methionine. Which intermediate does mutant 2 accumulate?

Accepted Answer

Cystathionine

Question 6

Which type of gene interaction allows a dominant allele from either gene to produce the wild-type phenotype, but requires homozygous recessive alleles at both genes for the mutant phenotype?

Accepted Answer

Duplicate gene interaction

Question 7

In a pathway with the following order: $$	ext{serine} ightarrow 	ext{cysteine} ightarrow 	ext{cystathionine} ightarrow 	ext{homocysteine} ightarrow 	ext{methionine}$$, a mutant accumulates cystathionine. Which enzyme is most likely defective?

Accepted Answer

The enzyme converting cystathionine to homocysteine

Question 8

Which of the following best describes recessive epistasis?

Accepted Answer

Mutant (recessive) alleles at one gene mask the expression of alleles at another gene.

Question 9

In a complementation test, five Neurospora mutants are crossed in all combinations. The results show two complementation groups: (1 & 4) and (2, 3, & 5). How many genes are responsible for the mutant phenotype?

Accepted Answer

Two

Question 10

A cross between DDww (red) and ddWW (white) foxgloves produces F1 plants with genotype DdWw (white). If you cross two F1 plants, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:4$$

Question 11

Which scenario is an example of dominant suppression epistasis?

Accepted Answer

A dominant allele at one gene suppresses the expression of the dominant allele at a second gene.

Question 12

In the arginine biosynthetic pathway in Neurospora, which mutant would be rescued by supplementation with citrulline but not ornithine?

Accepted Answer

A mutant defective in the enzyme converting ornithine to citrulline

Question 13

Which type of gene interaction produces a $$9:7$$ phenotypic ratio in the F2 generation?

Accepted Answer

Complementary gene interaction

Question 14

A mutant strain accumulates homoserine and can only grow on media supplemented with cysteine, cystathionine, homocysteine, or methionine. Which step in the pathway is blocked?

Accepted Answer

Conversion of homoserine to cysteine

Question 15

Which of the following is NOT a feature of a signal transduction pathway?

Accepted Answer

It is involved in pigment biosynthesis.

Question 16

In a dominant gene interaction, what is the expected phenotypic ratio if both genes contribute to the phenotype and each has a dominant allele?

Accepted Answer

$$9:6:1$$

Question 17

Which of the following best explains why genes rarely act on their own to produce wild-type phenotypes?

Accepted Answer

Genes require interaction with other genes for proper function.

Question 18

A mutant in the threonine biosynthetic pathway cannot grow on minimal media unless threonine is added. What does this indicate about the mutant?

Accepted Answer

It is an auxotroph for threonine.

Question 19

Which of the following is an example of a developmental pathway?

Accepted Answer

A network of genes involved in growth and development.

Question 20

In a biosynthetic pathway, which experimental approach is used to determine the order of intermediates?

Accepted Answer

Genetic dissection using single-gene mutants and supplementation with pathway intermediates.

Inheritance Patterns of Single Genes and Gene Interactions

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