Question

A female mouse that is homozygous for the \(A^{v}\) allele is mated to a male that is homozygous for a loss-of-function \((a)\) allele. How would you expect the diet of this female during pregnancy to affect her offspring? a. Dietary agents that promote a greater level of DNA methylation would produce offspring with more yellow fur. b. Dietary agents that promote a lower level of DNA methylation would produce offspring with more yellow fur. C. Dietary agents that promote a greater level of DNA methylation would produce offspring with darker fur. d. Dietary agents that promote a lower level of DNA methylation would produce of fspring with darker fur. e. Both b and c are correct.

Short answer

The correct answer to the problem is option e, which suggests that both dietary agents promoting a lower level of DNA methylation would produce offspring with more yellow fur and dietary agents promoting a greater level of DNA methylation would produce offspring with darker fur.

Step-by-step solution

Understand the genotypes of the parents

The mother mouse is homozygous for the \(A^{v}\) allele, which suggests that it has two copies of this allele. The father mouse is homozygous for a loss-of-function allele (a), having two copies of this allele. However, because the father's allele is a loss-of-function allele, variations in the mother's diet that affect DNA methylation will have a significant effect on the fur color of the offspring.

Understand the effect of DNA methylation on gene expression

DNA methylation typically inhibits or reduces gene expression. So, dietary agents promoting a greater level of DNA methylation would be expected to reduce the expression of the \(A^{v}\) gene. Since the \(A^{v}\) allele is presumably responsible for the yellow fur, reducing its expression would lead to less yellow fur or darker fur. On the other hand, if the diet promotes a lower level of DNA methylation, it would lead to increased expression of the \(A^{v}\) gene and thus, more yellow fur in the offspring.

Deduce the correct answer

Drawing from the understanding in Step 1 and Step 2, it becomes evident that dietary agents promoting a lower level of DNA methylation would produce offspring with more yellow fur. This leads us to the conclusion that option (b) is correct. On the contrary, dietary agents that promote a greater level of DNA methylation would reduce the expression of the \(A^{v}\) allele, producing offspring with darker fur, making option (c) also valid. Therefore, option (e) which presents both (b) and (c) as correct is the accurate answer.

Key concepts

Genetic Inheritance

Genetic inheritance refers to the transmission of genetic traits from parents to their offspring. When we talk about homozygous alleles, it means an organism carries two identical copies of a gene. For instance, the mouse in the exercise is homozygous for the \(A^{v}\) allele, possessing two copies of this allele. In genetic inheritance:

• "Dominant alleles" can overshadow the effects of "recessive alleles" when they are different (heterozygous).
• Homozygous alleles feature two similar alleles, either both dominant or both recessive.

In the example, the male mouse possesses a loss-of-function allele (a), which does not exhibit dominant traits. Consequently, the maternal alleles, \(A^{v}\), take the lead in determining the offspring's characteristics. Understanding these inheritance principles helps predict how different traits, such as fur color, might appear in the next generation. Genetic inheritance thus acts as a roadmap for the traits to be passed down, influencing everything from physical appearance to the potential susceptibility to certain ailments.

Fur Color Genetics

The genetics behind fur color in mice involves specific alleles or variations of genes that regulate pigmentation. For the mice in our scenario, the \(A^{v}\) allele influences fur color, likely producing yellow hair due to its genetic configuration.In the context of fur color genetics:

• Genes responsible for pigmentation can be significantly impacted by genetic combinations involving dominant and recessive alleles.
• The presence of dominant alleles generally manifests in observable traits, such as a specific fur color.
• Loss-of-function alleles typically do not influence the phenotype, especially when paired with a functioning dominant allele.

By pairing the \(A^{v}\) allele with the functionless allele (a), the \(A^{v}\) allele strongly influences the color outcome. This setting becomes even more interesting with factors like DNA methylation, which can further tweak gene expression, adding another layer of complexity to fur color determination. This interaction makes it clear why understanding genetics is pivotal—fur color is not just a straightforward matter of allele presence; it can be modulated by epigenetic factors too.

Gene Expression Regulation

Gene expression regulation is a crucial component when considering how genes influence traits like fur color. A vital mechanism in this regulation is DNA methylation, an epigenetic modification where methyl groups are added to DNA. This generally suppresses gene activity.In relation to gene expression:

• DNA methylation reduces the expression of genes by preventing gene transcription—the process in which DNA is converted into messenger RNA (mRNA).
• Factors such as diet can influence methylation, indicating external environments may impact genetic expression.
• An increased level of DNA methylation often leads to decreased gene activity and vice versa.

In the exercise, it's posed that dietary elements affecting DNA methylation could alter the expression of the \(A^{v}\) allele. More methylation would result in the suppression of \(A^{v}\), producing darker fur as the yellow-producing gene's activity diminishes. Conversely, lower methylation would leave gene expression unimpeded, resulting in more yellow fur due to the full expression of \(A^{v}\). Thus, controlling gene expression extends beyond genetic code, involving external modalities such as diet—a concept illustrating the dynamic nature of traits in organisms.