When a cell in a fully developed adult vertebrate synthesizes a protein, does it matter whether the mRNA transcribes the maternal or the paternal allele that codes for the protein? There are small differences in the base pair sequences of the two alleles. These differences would make small differences in the amino acid sequence of the resulting protein. Does the cell need to select which of the two alleles is to be transcribed, or are the differences too small to matter?
When a cell synthesizes a protein, it matters whether the mRNA comes from a maternal or a paternal allele of the gene that codes for the protein. This is because female mammals have an additional system for differential allele expression - ChrX inactivation. In a tissue, one ChrX is randomly inactivated by heterochromatisation. Therefore, most of the gene on one ChrX are off. That is why, some cells in a tissue will express the maternal allele, while others the parental allele.
Dear Del Eaton, if you have additional questions you can place new question or submit it as assignment.
What about alleles on genes other than those on ChrX? Do the small differences between paternal and maternal alleles that code for the same protein require the cell mechanism to select which of the two alleles the mRNA comes from?