Sex Determination and Differentiation in Vertebrates

Sex Determination and Differentiation in Vertebrates Umesh Rai and Brototi Roy Department of Zoology, University of Delhi Delhi-110007 The concept of sex determination and differentiation has been baffling mankind since time immemorial. While Aristotle hypothesized in 335 B.C. that sex was determined by the heat generated during conception, Andreas Vesalius in 1543 A.D illustrated that women were but males, their genitalia turned inside out. In numerous cultures since then, women have been considered as the “default state of men”. However, in the 17 th century gradually it was discovered that the females produced eggs that transmitted parental traits. Later, in the twentieth century Geddes and Thomson came forward with the hypothesis that constitution, age, nutrition and environment of parents decide the sex determination of the offspring. This environmental view of sex determination was again challenged by the discovery of sex chromosomes by McClung in 1902. Following this, more evidences gradually clinched to suggest the chromosomal concept of sex determination. Numerous experimental studies in vertebrates have now established beyond doubt that sex is determined either by chromosomal factors, environmental influences, or interplay of both, depending on the species/groups.