BICD 100 Lecture Notes - Lecture 8: Dosage Compensation, Sister Chromatids, X-Inactivation
1 Apr 2019
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Compensate for the different "dosage" of x chromosome in males and females. Worms express 1/2 as much x in hermaphrodites. Flies express twice as much x in males. Silence one female x chromosome so males and females express the same amount. Random inactivation of either the maternal or paternal chromosome. Occurs early in embryonic development, and all cellular descendants have the same inactivated chromosome. Either the paternal or maternal x chromosome is inactivated at random, and all progeny cells retain the inactivation. X inactivation is maintained through several cell divisions. Creates "clones" of groups of cells that have one chromosome inactivated. Female mammals are mosaics of x chromosome expression. We just discussed these unusual chromosomal arrangements in the context of sex determination. Meiosis 1 is key step: 2n to 1n. 2 sister chromatids for each of 2 chromosomes. Nondisjunction during meiosis causes variation in chromosome number. Aneuploidy occurs upon fertilization with haploid gamete week 5 page 1.
