Cells in the somatic tissues of metazoans have two or more copies of the genome, one provided by the sperm and one provided by the egg. Thus, there is a maternal and a paternal allele for each gene. Bias toward one allele or the other can be consequential, especially if one allele is dysfunctional/mutated. Allele expression bias is known to occur because of both stochastic and epigenetic processes. The Mendenhall lab is working to understand how allele expression bias occurs in different cell types (e.g., muscles or intestines). They have currently observed allele expression bias that is attributable to epigenetic processes, and also, some bias that is due to stochastic (chance based) processes.