Linkage analysis for mapping genes of sex-influenced traits.

Statistical methods are developed to estimate gender-specific and gender-average recombination frequencies between a biallelic or multiallelic marker and a sex-influenced gene. Iterative solutions are developed for intercross (or F-2 design). For biallelic markers, two iterative solutions are required, one for coupling and repulsion parental linkage phases and one for mixed parental linkage phases. For multiallelic markers, one set of iterative equations applies to all possible parental linkage phases. The resulting formulae for estimating recombination frequency use the full data set and yield estimates that are exactly the same as the true parameters if the observed and expected phenotypic distributions are equal. When one parent is homozygous for the sex-influenced gene as is expected with the backcross design, simple solutions exist for estimating recombination frequencies. However, offspring of one gender (male or female) do not have linkage information depending on whether the homozygous parent has two male-dominant or male-recessive alleles. Consequently, an F-2 design is more efficient than a backcross design for mapping a sex-influenced gene. Knowing each parental linkage phase is important to apply the methods developed in this article. It is shown that an individual's linkage phase of the sex-influenced locus can be determined based on allele transmission from the parents for all crosses except under the mating between an expressed male and an unexpressed female.