What genetic process is likely responsible for the occurrence of asthma in only one of a pair of identical twins?

The occurrence of asthma in only one of a pair of identical twins can be primarily attributed to epigenetic modifications. Identical twins share the same genetic makeup, yet their environments and experiences can lead to differences in gene expression. This phenomenon is central to epigenetics, where factors such as lifestyle, environmental exposures, and even stress levels can cause changes in how genes are turned on or off without altering the underlying DNA sequence.

Epigenetic modifications, such as DNA methylation and histone modification, can influence inflammation, immune responses, and other pathways relevant to asthma pathology. For example, if one twin is exposed to allergens or pollutants that the other is not, this exposure could lead to specific epigenetic changes that predispose only that twin to developing asthma.

Understanding that asthma can develop in one twin and not the other despite identical genes highlights the importance of considering not only genetic predisposition but also the role of external factors that influence gene expression—hence, emphasizing the significance of epigenetics in the development of complex diseases like asthma.