_Y_+30 _IMG_01_03-human_karyotype.jpg AligN=MiddlE This is a human male karyotype, a display of condensed chromosomes arranged in _Vid_karyo.swf pairs. Each chromosome consists of two sister chromatids joined at a centromere. Humans possess 23 pairs of chromosomes: one member of a pair is derived from each parent. 22 pairs are homologous and contain the same genes; the other 2 are sex-determining chromosomes: females are XX and males are XY.