The in vitro transmission frequency of the t⁶ allele

Abstract

The T region, located on chromosome 17 in the mouse, is a complex genetic locus which includes a series of recessive mutations, tⁿ (refs 1, 2). These mutations include several alleles (also referred to as t-haplotypes²) which are embryonic lethals (t^L). An additional phenotypic expression of the recessive lethal mutations is a distorted transmission of the t allele by the heterozygous male parent. Most T/t^L and +/t^L males transmit the recessive mutation to over 50% of their offspring. Two conditions are known to modify significantly the transmission frequency of some t^L alleles: the length of time between insemination and fertilisation^3–5 and the genetic background of the female⁶. The present studies were undertaken to determine if the distorted transmission frequency of one of the lethal alleles, t⁶, could be reproduced in vitro. The data show that the in vitro transmission frequency of the t⁶ mutation is non-mendelian and is not significantly different from the frequency of transmission of this mutation following in vivo delayed matings. The in vitro frequency is, however, significantly lower than the normal mating frequency and does not vary as a function of incubation time. These data suggest that the observed delayed and normal mating frequency differences result from time-dependent interactions between the t⁶-bearing spermatozoon and the female reproductive tract.