Determination of sex in humans was discussed in Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting
and it was pointed out that the presence of Y Chromosome determines maleness and its absence determines femaleness. This situation resembles the condition recorded in plants like Coccinia
and is different from the condition known in Drosophila.
Consequently, males are XY and females are XX in human beings.
Recently (in 1986) rare cases have been reported where males have been found to be XX and females were found to be XY. These can be due to one of the following two reasons - (i) A sex reversal gene SRY
located on the Y-chromosome, leads to XX males and XY females. (ii) Translocation of a small segment of Y-chromosome (lying close to centromere on short arm), to an X chromosome in XX males and its deletion from the Y chromosome (or mutation in SRY
)in XY females. As a result of these XX males and XY females, it could be established that male determining factor is located on the short arm of Y-Chromosome, in the region 1A. More details on recent developments in the area of sex determination and sex differentiation using the techniques of molecular biology were discussed in Sex Determination, Sex Differentiation, Dosage Compensation and Genetic Imprinting