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Lyon hypothesisan explanation for DOSAGE COMPENSATION in the X-chromosomes of mammals including humans, proposed by Mary Lyon. The main features of the hypothesis are that only one X-chromosome is active in a mature mammalian cell, all other X-chromosomes present having been inactivated during embryological development. Different X-chromosomes are thought to be inactivated in different cells, which may produce a MOSAIC phenotype in heterozygous individuals. BARR BODIES are thought to indicate the presence of inactive X-chromosomes.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005