Information on the nature of t-haplotypes from the interaction of mutant haplotypes in male fertility and segregation ratio

Abstract

The t-haplotype t6 interacts with brachyury, T, to produce taillessness, and exhibits lethality, male sterility and high male segregation ratio. Mutant haplotypes derived from t6 which have lost the lethality also lose the sterility. We here report that two mutants which have retained the lethality have also retained the sterility and suggest that the two properties of lethality and sterility are due to a factor or region of the t-haplotype located close to the locus of tf. Although t6 has a high male segregation ratio, mutants derived from it may have low or normal ratios. In trans heterozygotes of two mutant haplotypes the ratios tended to be equalized, whereas in cis heterozygotes a high ratio like t6 was obtained, at least in one case. On this evidence the low-ratio gene Low is reinterpreted as a mutant t-haplotype and designated tlow. It is suggested that abnormal ratio is due to an A-factor or region located between the loci of T and tf, so that t6 carries T-, A- and LS-factors which can exist separately and retain their properties. t6 may extend less proximally than other natural t-haplotypes, which in general may involve changes in interstitial heterochromatin. © 1977, Cambridge University Press. All rights reserved.