Chromosomal theory of sex determination The X-chromosome was first observed by the German biologist, Henking in 1891 during the spermatogenesis in male bug and was described as X-body. The chromosome theory of sex determination was worked out by E.B. Wilson and Stevens (1902-1905). They named the X and Y chromosomes as sex-chromosomes or autosomes and other chromosomes of the cell as autosomes. Sex chromosomes carry genes for sex. X-chromosomes carries female determining genes and Y-chromosomes has male determining genes. The number of X and Y chromosomes determines the female or male sex of the individual, Autosomes carry genes for the somatic characters. These do not have any relation to sex. Sex determination in Drosophila"- Although both mammals and fruit flies produce XX females and XY males, their chromosomes achieve these ends using very different means. The sex-determining mechanisms in mammals and in insects such as Drosophila are very different. In mammals, the Y chromosome plays a pivotal role in determining the male sex. Thus, XO mammals are females, with ovaries, a uterus, and oviducts (but usually very few, if any, ova). In Drosophila, sex determination is achieved by a balance of female determinants on the X chromosome and male determinants on the autosomes. Sex determination in Grasshopper"- There is only one sex chromosome, referred to as X. Males only have one X chromosome (X0), while females have two (XX). Maternal gametes always contain an X chromosome, so the sex of the animals' offspring depends on whether a sex chromosome is present in the male gamete.