Question 1

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

Accepted Answer

Each gene encodes a single enzyme that affects a single step in a metabolic pathway.

Question 2

In a biosynthetic pathway for methionine synthesis, a mutant strain of Neurospora can only grow on minimal media supplemented with homocysteine or methionine, but not with cysteine or cystathionine. Which step in the pathway is most likely blocked in this mutant?

Accepted Answer

The conversion of homocysteine to methionine.

Question 3

A prototroph is defined as:

Accepted Answer

A strain that can synthesize all compounds required for growth from minimal media.

Question 4

You perform a complementation test between two Neurospora mutants unable to synthesize arginine. The diploid grows on minimal media. What does this indicate?

Accepted Answer

The mutations are in different genes.

Question 5

In a genetic pathway, if mutant 1 accumulates compound B and grows only when supplied with compound C or later, while mutant 2 accumulates compound C and grows only when supplied with compound D or later, what is the correct order of intermediates?

Accepted Answer

$A \rightarrow B \rightarrow C \rightarrow D$

Question 6

Which type of gene interaction is described when a dominant allele at either of two genes produces the wild-type phenotype, and only the double homozygous recessive shows the mutant phenotype?

Accepted Answer

Duplicate gene interaction

Question 7

In a dihybrid cross involving two genes with recessive epistasis, what phenotypic ratio is expected in the F2 generation?

Accepted Answer

$9:3:4$

Question 8

A summer squash plant with genotype $WwYy$ is crossed with another $WwYy$ plant. If $W$ is dominant epistatic to $Y$, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$12:3:1$

Question 9

In a complementation test, five mutants are tested in all pairwise combinations. The results show two complementation groups. Which of the following best explains this result?

Accepted Answer

There are mutations in two different genes.

Question 10

A cross between two true-breeding foxglove plants, one red ($DDww$) and one white ($ddWW$), produces F1 plants that are all white. If these F1 plants are self-crossed, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$12$ white : $3$ red : $1$ pink

Question 11

Which of the following best describes epistasis?

Accepted Answer

An interaction where alleles at one gene mask or modify the expression of alleles at another gene.

Question 12

In a pathway for pigment production in Drosophila, the brown and vermilion genes are both required for pigment synthesis, while the white gene is required for pigment transport. What phenotype would you expect in a fly with mutations in both brown and white genes?

Accepted Answer

White eyes

Question 13

A strain of Neurospora is auxotrophic for arginine. It can grow on minimal media supplemented with citrulline or arginine, but not with ornithine. Which enzyme is most likely defective?

Accepted Answer

The enzyme converting ornithine to citrulline.

Question 14

Which of the following is an example of dominant suppression?

Accepted Answer

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

Question 15

In a genetic dissection experiment, four mutants are isolated, each accumulating a different intermediate in the methionine pathway. Which experimental approach allows you to determine the order of intermediates?

Accepted Answer

Supplying each mutant with different pathway intermediates and observing growth.

Question 16

A mutant strain of yeast can grow on minimal media supplemented with compound X or Y, but not with compound W. Which of the following is most likely true?

Accepted Answer

The mutation blocks the conversion of W to X.

Question 17

Which of the following best explains why two mutants with the same phenotype may complement each other?

Accepted Answer

The mutations are in different genes required for the same pathway.

Question 18

In a signal transduction pathway, what is the primary role of the network of genes involved?

Accepted Answer

To regulate the expression of a target gene in response to a signal.

Question 19

If a mutant accumulates cystathionine and grows only when supplied with homocysteine or methionine, which enzyme is most likely defective?

Accepted Answer

The enzyme converting cystathionine to homocysteine.

Inheritance Patterns of Single Genes and Gene Interactions

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