A sex-ratio meiotic drive system in Drosophila simulans

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The X-linked Dox gene first evolved to target an unknown component of the Y chromosome, so that Y-bearing sperm fail to develop. This leads to an increased transmission frequency of the Dox-bearing X chromosome and a female-biased sex ratio. It remains unclear whether Dox is an RNA or protein-coding gene. Later, a transposition of Dox to Chromosome 3 created the Nmy gene. siRNAs produced from the doublestranded hairpin of Nmy target the homologous region of Dox for degradation via the RNAi pathway. As a result, Y-bearing sperm develop normally, and X-chromosome meiotic drive is suppressed. The model depicts a pre-meiotic germ cell, but the cellular manifestation of distortion occurs during nuclear condensation and maturation of sperm. Only the sex and third chromosomes are shown. Credit: Ferree et al.

If you met a person who had 10 children, all of whom were girls, you would probably find this surprising. Yet this kind of distorted sex ratio does occur in groups as diverse as mammals, insects, and plants, where some parents consistently produce litters in which the sex ratio is dramatically skewed. For the first time, Yun Tao and colleagues report, in this week’s issue of the open-access journal PLoS Biology, the identification of both a fly gene that can create these skewed ratios and the counter-gene, found in most of the fly population, which suppresses such distortion.

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All News summaries for November 06, 2007