sex chromosome defined in 1951 yearsex chromosome - sex chromosome;
sex chromosome - Chromosomes of which there is a homologous pair in the nuclei of one sex (the homogametic sex), and a dissimilar pair (or an unpaired chromosome) in those of the other (the heterogametic sex). The sex chromosomes which occur as a pair in the homogametic sex are called X-chromosomes. The heterogametic sex has an X-chromosome and either a Y-chromosome or none. The homogametic (or XX) sex produces gametes which arc identical in their sets of chromosomes, all containing one X-chromosome. The heterogametic (XY or XO) sex produces equal numbers of two different sorts of gametes, one with and one without an X-chromosome. Union of the gametes of the XX sex with those of the XY (or XO) sex therefore results in offspring consisting of approximately equal numbers of the two sexes. The presence or absence of a Y-chromosome determines sex in mammals; in insects it is determined by the number of X-chromosomes in relation to the number of autosomes. The sex-determining mechanism is of course absent in hermaphrodite animals and plants.
near sex chromosome in Knolik
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