Abstract
Genetically specified body odors are termed odor types. We showed previously that both the X chromosome and the Y chromosome of the mouse determine differential odor types demonstrable by the behavior of trained mice in the conventional Y-maze test system extensively used in the definition of odor types specified by the major histocompatibility complex (MHC). In the present studies we aimed to ascertain whether perception of X chromosomal and Y chromosomal odor types, like the perception of MHC odor types, exerts a spontaneous influence on reproduction. By making use of reciprocal F1 hybrid males and males of the congenic B6.YAKR strain, males differing solely in their X chromosomes, their Y chromosomes, or both were tested in the conventional pregnancy-block system in which isolated females in early pregnancy are known to be subject to a heightened incidence of failed pregnancy when confronted with the scent of a male whose MHC type differs from that of the missing stud male. As previously established for MHC disparity, perception of X chromosomal disparity or of Y chromosomal disparity between stud and secondary males caused a highly significant rise in the incidence of terminated pregnancy. Thus perception of differential odor types other than those specified by the MHC may also be concerned in aspects of selective reproduction.