Sex determination in animals

The medium size chromosome in drosophila melanogaster determines the individual’s sex for which reason they are called the sex chromosome. In the female, the two sex-chromosome, both rod-shaped in appearance, are identical and are known as X-chromosomes. In the male, however, the two sex-chromosome differ from each other one is a rod-shaped X-chromosome, the other is a hook-shaped, and is called Y-chromosome. The sex chromosomes are the exception to the rule that homologous chromosomes are identical in appearance. Being different they are described as heterosomes; All the other chromosomes, which are identical in appearance, are called autosomes. Despite this difference, the sex chromosomes are transmitted in a normal mendelian manner as shown below.

Generally, a female produces only one kind of gamete as the chromosomes are concerned; all her eggs contain an X chromosome. For this reason, inhuman and many other species, the female is said to be homogametic (same gametes). A male on the other produces two kinds of gametes as far as chromosome are concerned: half of the sperm contains a Y chromosome, the other half an X. The male is therefore heterogametic (different gametes) on fusing randomly, approximately half the zygotes receive two X chromosomes and develop into the female, the rest receive Y chromosomes and give rise to males. In some insects, females are XX and male XO Please find free downloadable notes, exams and marking guides of agriculture, biology, Physics, chemistry etc.  from digitalteachers.co.ug website. Dr. Bbosa Science