Measuring segregation distortion in Drosophila melanogaster

Abstract

Segregation distorter (SD) chromosomes are preferentially transmitted to offspring of a male heterozygous for SD and SD+ chromosomes, as a result of the dysfunction of SD+-bearing sperm. Segregation distortion is measured by the segregation ratio k, the proportion of progeny bearing the SD chromosome. However, k is an ordinal measure and is therefore of only limited usefulness. A transformation has been developed (the k-probit transformation) that has been used to provide an interval method of measuring segregation distortion. This method has not been adequately tested as previous comparisons of observed k distributions with those predicted by the k-probit transformation have not taken the effects of binomial sampling into consideration. We have compared k distributions produced by three different SD chromosomes with the k distributions predicted by the k-probit transformation, utilizing a computer simulation model to account for binomial sampling. The results observed with two of the SD chromosomes do not agree with the predictions of the transformation. Thus we do not support the use of the k-probit transformation to provide a valid interval measure for segregation distortion.Key words: segregation distortion, Drosophila.