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Mechanistic and Evolutionary Model for Sex-ratio Distortion

Caption: 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.

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