Definition of Lyon Hypothesis

Lyon hypothesis is a hypothesis that explains the inactivation of X-chromosomes in mammals. Despite being active at the early stage of embryonic development, one out of the two X-chromosomes becomes inactivated in the somatic cell. The two X-chromosomes in the females and only one in the case of males are compensated by the inactivation of one of it in the somatic cells of the females.


Hence, this hypothesis states the gene dosage imbalance that exists between the males and the females. The inactive X-chromosome is wrapped up in the heterochromatin which is a transcriptionally inactive structure. This inactivation of the X-chromosome remains throughout the life span of the cell and is moved on to the descendants as well.

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