Sex Dosage Compensation in Drosophilia
In mammals, the X and Y chromosomes differ greatly in gene content, as the X chromosome is quite large and contains roughly over a thousand genes (with the Y chromosome containing less than a hundred); so to equalize the dose of gene product (the ratio of autosome to X chrmosome), life has evolved a dosage compensation mechanism to keep the ratio between males and females equal. 
In Drosophilia, dosage compensation occurs by doubling the transcription rate (hypertranscription) of X-linked genes in males. Shown above are giant polytene chromosomes from the salivary glands, with the male-specfic lethal (MSL) complex labelled with specific antibodies in red and the rest of the DNA stained with Hoechst. There’s precise localization to the X-chromosome, where it significantly catalyzes (alongside the roX RNA the MSL contains) histone modification for gene regulation (specifically acetylation).
In our own species, females regulate dosage compensation by X-inactivation, and therefore every somatic cell has one random X-chromosome silenced (in what’s called a Barr body), with every cell descending from it sharing the same silenced X. 
This is what’s responsible for only female calico cats (males that are XXY are sterlie) having a tortoiseshell coat.

Sex Dosage Compensation in Drosophilia

In mammals, the X and Y chromosomes differ greatly in gene content, as the X chromosome is quite large and contains roughly over a thousand genes (with the Y chromosome containing less than a hundred); so to equalize the dose of gene product (the ratio of autosome to X chrmosome), life has evolved a dosage compensation mechanism to keep the ratio between males and females equal. 

In Drosophilia, dosage compensation occurs by doubling the transcription rate (hypertranscription) of X-linked genes in males.

Shown above are giant polytene chromosomes from the salivary glands, with the male-specfic lethal (MSL) complex labelled with specific antibodies in red and the rest of the DNA stained with Hoechst. There’s precise localization to the X-chromosome, where it significantly catalyzes (alongside the roX RNA the MSL contains) histone modification for gene regulation (specifically acetylation).

In our own species, females regulate dosage compensation by X-inactivation, and therefore every somatic cell has one random X-chromosome silenced (in what’s called a Barr body), with every cell descending from it sharing the same silenced X. 

This is what’s responsible for only female calico cats (males that are XXY are sterlie) having a tortoiseshell coat.

(Source: dev.biologists.org)

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Posted on Monday, 29 July
Tagged as: DNA   polytene chromosomes   Drosophilia   dosage compensation   gene expression   gene regulation   model organism monday   science  
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