In genomic imprinting, how can allele expression differ?

In genomic imprinting, the expression of alleles can differ based on the parent that contributed them, which is why the correct answer is that it varies according to parental origin. In this process, certain genes are "marked" or "imprinted" during gamete formation, resulting in the selective silencing of either the maternal or paternal allele in the offspring. This means that regardless of having the same genetic code, the imprinted alleles will lead to different phenotypic outcomes depending on which parent passes the allele to the offspring.

This phenomenon explains why an offspring might express a trait associated with one parent while the other parent's corresponding trait remains silent. The intricate regulation of gene expression due to genomic imprinting is crucial in various developmental processes and has significant implications in genetic diseases, inheritance patterns, and overall organismal development.