Concept:Sex determination is the mechanism which determines the biological sex of an individual.Henking (1891) had observed a nuclear structure throughout the spermatogenesis process in few insects and named it X-body.He also observed that after spermatogenesis, half of the sperms received this X-body and half of them did not.It was later found that this X-body was a chromosome and hence it became the X-chromosome.As the X-chromosome is involved in the sex determination process, it is termed as a sex chromosome.The other chromosomes that are not involved in sex determination are known as autosomes.Important PointsSex Determination Types -Male Heterogamety -Males produce 2 different types of gametes, while the female produces a single type of gamete.This can again be of 2 types -XX/XY type - The females possess a pair of X-chromosomes, while the males possess one X-chromosome and one Y-chromosome. E.g.- Man, Drosophila.XX/XO type - The females possess a pair of X-chromosomes, but the males posses only one X-chromosome, thus having one less chromosome than the females. E.g.- Grasshopper.Female Heterogamety -In this type, the females produce 2 different types of gametes, while the males produce a single type of gamete.This is observed in some birds.Here, the sex chromosomes are denoted as ZZ and ZW in males and females respectively.Therefore, the sex determination type is known as ZW/ZZ type.