SEX DETERMINATION IN DROSOPHILA

Sex determination in Drosophila-
( By the ratio of x chromosomes to autosomes)

If X/A= 1 (female) XX:2A
If X/A =0.5 (male)XY:2A

1.XX genotyes-

In such embryos the Sxl Gene activated and produces a protein called Sxl protein.Which cause the splicing of tra pre mRna at a downstream 3' splice site and the termination codon is spliced out with the intron, which leads to production of tra protein. Tra protein interacts with Tra-2 proteins and together they direct the female specific splicing of dsx pre-mRNA ,which produces proteins that cause the embryo into a female .
( It is regulated in post transcriptional level).

2. XY genotyes-

In such embryos the sxl Gene is not activated and the sxl protein is not produced. So,tra premRNa spliced at an upstream site resulting in the inclusion of a premature stop codon in the mRNA producing a non functional Tra protein .

Without functional Tra the male specific splicing of dsx pre-mRNA takes place which produces male Dsx proteins that cause the embryo to develop into a male .

(Sxl- sex lethal 

Tra -Transformer
dSX-Double sex )

IMAGE SOURCE CREDIT-http://www.biocyclopedia.com/index/genetics/images/figure/f17.12.jpg

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