Q.Differentiate Intersexes from Supersexes.

In Drosophila, sex is not fixed by the presence or absence of a Y chromosome the way it is in humans — the Y is needed only for male fertility, not for maleness itself. C.B. Bridges' 1921 triploid-female x diploid-male cross showed instead that sex is set by a balance: femaleness genes on the X chromosome are weighed against maleness genes on the autosomes, expressed as a sex index, $\text{Sex index} = \dfrac{\text{Number of X chromosomes}}{\text{Number of autosome sets}}$.

A sex index of 1.0 or higher (achieved by normal diploid, triploid, tetraploid or haploid flies alike, since it is the ratio that matters, not the absolute chromosome count) gives a female; an index of 0.50 or below gives a male; an index of exactly 0.67 (2X : 3A) gives a true intersex, showing a genuine mixture of male and female structures; and the extremes — metamales at 0.33 and metafemales at 1.5 — are viable but usually very weak and sterile. A related but distinct condition, the gynandromorph, is an individual whose different body parts are bui …