In mammals, sex is determined chromosomally rather than environmentally: of the diploid complement, 22 pairs are homologous autosomes and one pair is the non-homologous sex chromosomes, with XY producing a male and XX a female because a single gene on the Y (SRY) initiates development of male gonads. Because the female parent can contribute only an X while the male parent contributes either an X or a Y, offspring sex is determined entirely by the paternal gamete, and a Punnett square over the sex chromosomes predicts an equal expected ratio of the two sexes. The X carries many genes unrelated to sex determination, so recessive alleles on it show X-linked (sex-linked) inheritance: hemizygous males express the phenotype with a single copy while females must be homozygous, giving population incidences of m in males and approximately m² in females for allele frequency m. The topic belongs to genetics, specifically chromosomal sex determination and non-Mendelian inheritance patterns.
In mammals, sex is determined chromosomally rather than environmentally: of the diploid complement, 22 pairs are homologous autosomes and one pair is the non-homologous sex chromosomes, with XY produ…