Q: Which equation correctly calculates penetrance if 8 out of 10 individuals with a dominant allele show the phenotype?

$$\text{Penetrance} = \frac{8}{10} = 0.8 = 80\%$$

Question 1

Which of the following best describes a haplosufficient gene?

Accepted Answer

A gene where one functional allele is sufficient to produce the wild-type phenotype.

Question 2

A patient is heterozygous for a gene with a dominant negative mutation affecting a multimeric protein. What is the most likely outcome for the protein function?

Accepted Answer

The protein will be nonfunctional due to abnormal interactions between mutant and wild-type subunits.

Question 3

Which equation correctly calculates penetrance if 8 out of 10 individuals with a dominant allele show the phenotype?

Accepted Answer

$$	ext{Penetrance} = \frac{8}{10} = 0.8 = 80\%$$

Question 4

A cross between two yellow mice (genotype $$A^Y A) $$produces offspring in a 2:1 ratio of yellow to agouti. What explains the absence of $$A^Y A^Y$$ offspring?

Accepted Answer

The $$A^Y$$ allele is recessive lethal, so $$A^Y A^Y$$ individuals die early in development.

Question 5

Which of the following is an example of codominance in humans?

Accepted Answer

The MN blood group, where both M and N antigens are expressed in heterozygotes.

Question 6

A gene mutation results in a protein with a new function not seen in the wild-type. What type of mutation is this?

Accepted Answer

Neomorphic mutation

Question 7

In a dihybrid cross, you observe a 9:7 phenotypic ratio in the F2 generation. What is the most likely explanation?

Accepted Answer

Complementary gene interaction, where both genes are required for the final phenotype.

Question 8

A woman with genotype $$I^A I^B$$ for the ABO blood group has a child with genotype $$I^A i. $$What is the possible genotype of the father?

Accepted Answer

$$I^A i$$

Question 9

Which of the following best describes variable expressivity?

Accepted Answer

Individuals with the same genotype may show different degrees or combinations of a phenotype.

Question 10

In the methionine biosynthetic pathway, a mutant strain grows on minimal medium supplemented with cystathionine but not with cysteine. Which gene is most likely mutated?

Accepted Answer

Met 3

Question 11

A cross between two rabbits, one with genotype $$C^ch C ($$chinchilla) and one with genotype $$C^h C ($$Himalayan), produces offspring in a 1:2:1 ratio. What does this indicate about the relationship between the $$C^ch$$ and $$C^h$$ alleles?

Accepted Answer

$$C^ch is $$partially dominant to $$C^h ($$incomplete dominance).

Question 12

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

Accepted Answer

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

Question 13

Which of the following is an example of a pleiotropic gene effect?

Accepted Answer

A gene mutation that causes both hearing loss and different-colored eyes.

Question 14

A man with genotype $$Rh^+ Rh^-$$ and a woman with genotype $$rr$$ have a child. What is the probability that the child will be Rh negative?

Accepted Answer

$$0.5$$

Question 15

Which of the following best describes a gain-of-function hypermorphic mutation?

Accepted Answer

A mutation that results in increased gene activity compared to wild-type.

Question 16

In a genetic pathway, which type of gene interaction is indicated by a 15:1 phenotypic ratio in the F2 generation?

Accepted Answer

Duplicate gene interaction

Question 17

A woman with polydactyly (autosomal dominant) has a child with the same genotype but no extra digits. What genetic concept does this illustrate?

Accepted Answer

Incomplete penetrance

Question 18

Which of the following is true about loss-of-function mutations?

Accepted Answer

They are usually recessive but can be dominant in the case of dominant negative mutations.

Question 19

In a complementation test, two mutants with the same phenotype are crossed and produce wild-type offspring. What does this indicate?

Accepted Answer

The mutations are in different genes.

Gene Interactions and Functional Effects of Mutations

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