Monoalleelinen

Monoalleelinen is a term used in genetics to describe a condition where only one allele is present for a particular gene. Alleles are different versions of the same gene. Typically, an individual inherits two alleles for each gene, one from each parent. However, in monoallelic expression, only one of these two alleles is actively transcribed and translated into a protein. This means that the information from only one allele is used to determine a trait or function.

This phenomenon can occur in several ways. One common mechanism is genomic imprinting, where specific genes are marked (either by methylation or other epigenetic modifications) to be silenced depending on whether they are inherited from the mother or the father. Another cause of monoallelic expression is X-chromosome inactivation in females. In female mammals, one of the two X chromosomes is randomly inactivated early in development to equalize gene dosage with males who have only one X chromosome. This inactivation leads to monoallelic expression of most genes on the X chromosome in any given cell.

Random monoallelic expression can also occur for genes on autosomes (non-sex chromosomes) without known imprinting or X-inactivation. The reasons for this are not always fully understood but can involve complex regulatory mechanisms. The consequence of monoallelic expression is that the phenotype associated with the gene is determined by the activity of a single allele, rather than the combined effect or interaction of both. This can have implications for genetic variability, disease susceptibility, and developmental processes.