Segregation ratios within Segregation Distorter lines of Drosophila melanogaster conform to a beta-binomial distribution.
Segregation Distorter (SD) chromosomes are preferentially recovered from SD/SD+ males due to the dysfunction of sperm bearing the SD+ chromosome. The proportion of offspring bearing the SD chromosome is given the symbol k. The nature of the frequency distribution of k was examined by comparing observed k distributions produced by six different SD chromosomes, each with a different mean, with k distributions predicted by two different statistical models. The first model was one where the k of all males with a given SD chromosome were considered to be equal prior to the determination of those gametes which produce viable zygotes. In this model the only source of variation of k would be binomial sampling. The results rigorously demonstrated for the first time that the observed k distributions did not fit the prediction that the only source of variation was binomial sampling. The next model tested was that the prior distribution of segregation ratios conformed to a beta distribution, such that the distribution of k would be a beta-binomial distribution. The predicted distributions of this model did not differ significantly from the observed distributions of k in five of the six cases examined. The sixth case probably failed to fit a beta-binomial distribution due to a major segregating modifier. The demonstration that the prior distribution of segregation ratios of SD lines can generally be approximated with a beta distribution is crucial for the biometrical analysis of segregation distortion.
Sharp
C B
CB
Department of Molecular Biology and Genetics, University of Guelph, Ontario, Canada.
Hilliker
A J
AJ
D000818:Animals; D002875:Chromosomes / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics*; D005796:Genes; D008297:Male; D008540:Meiosis; D008957:Models, Genetic; D015233:Models, Statistical; D010641:Phenotype