AAMC FL Practice Exam

What are imprinted genes?

1. Genes that can only express in the presence of certain nutrients

2. Genes whose expression is influenced by environmental factors

3. Genes whose expression is determined by the parent that contributed them

4. Genes that have no functional role

The correct answer is: Genes whose expression is determined by the parent that contributed them

Imprinted genes are particularly interesting because their expression is regulated by the parent of origin, meaning that the gene inherited from one parent may be expressed while the gene from the other parent is silenced. This unique mechanism of gene regulation plays a crucial role in development and growth, as it can affect phenotype based on which parent's allele is active. This parent-specific expression occurs due to epigenetic modifications, such as DNA methylation and histone modification, that mark the genes during gametogenesis. As a result, if a gene is imprinted from the paternal side, only the maternal allele will be expressed, or vice versa. This has significant implications for genetic inheritance and can lead to various genetic disorders when the imprinting process is disrupted. In contrast, the other choices do not correctly describe imprinted genes. Some choices discuss expression influenced by nutrients or environmental factors, which are unrelated to the unique parent-dependent expression that characterizes imprinting. Other options imply a lack of functionality, which is inaccurate since imprinted genes often play crucial roles in development and growth processes.