Q: Which of the following equations correctly calculates penetrance?

$$\text{Penetrance} = \frac{\text{Number showing mutant phenotype}}{\text{Total number}} \times 100$$

Question 1

A cross between two heterozygous yellow mice (Yy) produces a 2:1 ratio of yellow to non-yellow offspring. Which genetic phenomenon best explains this result?

Accepted Answer

Lethal allele

Question 2

Which of the following best describes penetrance?

Accepted Answer

The percentage of individuals with a genotype who show the expected phenotype

Question 3

A geneticist observes that a mutation causes a disease in 85 out of 100 individuals who carry the mutant allele. What is the penetrance of this mutation?

Accepted Answer

$$85\%$$

Question 4

Which of the following scenarios is an example of epistasis?

Accepted Answer

The expression of one gene masks the expression of another gene

Question 5

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

Accepted Answer

$$9:7$$

Question 6

A woman with a dominant mutation for early-onset porphyria has children with a man who does not carry the mutation. The disease shows variable expressivity. Which of the following is most likely to be observed in their children?

Accepted Answer

Some children may have severe symptoms, others mild, and some may show no symptoms

Question 7

Which of the following best describes a sex-influenced trait?

Accepted Answer

A trait that is expressed differently in males and females due to hormonal differences

Question 8

A gene for coat color in mice is only expressed when the animal is exposed to a certain temperature range. This is an example of:

Accepted Answer

Temperature-sensitive mutation

Question 9

Which of the following is an example of dominant epistasis?

Accepted Answer

A dominant allele at one locus masks the expression of alleles at a second locus

Question 10

A plant breeder observes a 9:7 ratio in the F2 generation when crossing two pure-breeding lines. Which genetic interaction is most likely responsible?

Accepted Answer

Complementary gene interaction

Question 11

Which of the following best explains why some individuals with a disease-causing genotype do not show symptoms of the disease?

Accepted Answer

Incomplete penetrance

Question 12

A genetic disorder shows increased severity and earlier onset in successive generations. This phenomenon is known as:

Accepted Answer

Genetic anticipation

Question 13

Which of the following would most likely modify the expected 9:3:3:1 Mendelian ratio in a dihybrid cross?

Accepted Answer

Linkage between the two genes

Question 14

A gene is said to be hypostatic when:

Accepted Answer

Its expression is masked by another gene

Question 15

Which of the following equations correctly calculates penetrance?

Accepted Answer

$$	ext{Penetrance} = \frac{	ext{Number showing mutant phenotype}}{	ext{Total number}} 	imes 100$$

Question 16

A mutation in an essential gene is most likely to result in:

Accepted Answer

Lethality

Question 17

Which of the following is an example of gene interaction?

Accepted Answer

Two genes interact to produce a phenotype not seen in either parent

Question 18

A trait is only expressed in males, even though the gene is present in both sexes. This is an example of:

Accepted Answer

Sex-limited inheritance

Question 19

Which of the following best describes variable expressivity?

Accepted Answer

The same genotype produces different degrees of phenotype among individuals

Question 20

A mutation that prevents the synthesis of a nutrient molecule, resulting in disease only when the nutrient is absent from the diet, is an example of:

Accepted Answer

Nutritional mutation

Gene Interactions, Lethal Alleles, Epistasis, and Phenotypic Variation

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