Between-family variation in sex ratio in the Trinidad (T-30) strain of Aedes aegypti (L.) indicating differences in sensitivity to the meiotic drive gene M D

1573-6857

Springer Online Journal Archives 1860-2000

Biology

Sex ratio in the Trinidad (T-30) strain of Aedes aegypti has remained constant at around 43%♀ during seventeen years of laboratory culture. The divergence from 50% is due to meiotic drive by the M D gene on the Y chromosome. The driving Y chromosome gives a much more distorted sex ratio (mean = 5.7%♀) when coupled with the highly sensitive X chromosomes from strain 64. This was demonstrated in all of 98 families tested, indicating that all or most of the Y chromosomes in T-30 carry the M D gene. Consequently the low level of sex ratio distortion in T-30 must be due to resistance to M D. Crosses made within T-30 demonstrated wide differences in sex ratio between families, depending on the sensitivity of the male parent's X chromosome to M D. However, sex ratios were not continuously variable but fell within fairly discrete categories. Thus, X chromosomes could be classified according to the modal sex ratios associated with them: m s3 (12.5%♀), m s2 (32.5%♀), m s1 (40%♀), m r1 (47.5%♀) m r2 (57.5%♀). The different sex ratio categories were more discrete in the families of sib matings than from random matings, suggesting the possibility of background modification of what is essentially a balanced polymorphism. Evidence is presented suggesting that the polymorphism could be due to interaction at two loci. A further X variant, m s4 (〈10%♀) characterised strain 64 but was absent from T-30. A comparison of fertility between the different sex ratio categories in T-30 established that sex ratio distortion was not caused by differential mortality after fertilisation.

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