NONRANDOM FERTILIZATION IN MICE CORRELATES WITH THE MHC AND SOMETHINGELSE

One evolutionary explanation for the success of sexual reproduction as sumes that sex is an advantage in the coevolutionary arms race between pathogens and hosts. Accordingly, an important criterion in mate choi ce and maternal selection thereafter could be the allelic specificity at polymorphic loci involved in parasite-host interactions, e.g. the M HC (major histocompatibility complex). The MHC has been found to influ ence mate choice and selective abortions in mice and humans. However, it could also influence the fertilization process itself, i.e. (i) the oocyte's choice for the fertilizing sperm, and (ii) the outcome of th e second meiotic division after the sperm has entered the egg. We test ed both hypotheses in an in vivo fertilization experiment with two inb red mouse strains congenic for their MHC. The genotypes of the resulti ng blastocysts were determined by polymerase chain reaction. We found nonrandom MHC combinations in the blastocysts which may result from bo th possible choice mechanisms. The outcome changed significantly over time, indicating that a choice for MHC combinations during fertilizati on may be influenced by one or several external factors.