Inversion heterozygosity and the origin of XO daughters of Bpa/+ female mice

Abstract

THERE has long been an interest in developing mouse stocks carrying chromosome inversions for mutation testing. This interest stems from the fact that heterozygosity for a paracentric inversion, that is, a structural rearrangement in which a chromosome segment that does not include the centromere is rotated through 180°, results in suppression of recombination in the inversion region. This is caused by the failure of recovery of the products of single crossovers in this region, because dicentric chromatids and acentric fragments are produced that either fail to give functional meiotic products or result in the formation of unbalanced zygotes which are generally eliminated. Recombination between the pair of chromosomes concerned is, therefore, confined to any crossovers in the non-inverted regions and to the rare two-strand double crossovers which may occur within the inversion region if it is a long one. This property of inversion heterozygotes enables the recovery, in the progeny, of the structurally normal homologue largely intact and any recessive mutation located on it can be readily detected if suitable genetically marked stocks are used. In the simplest case, when the mutation is a recessive lethal and the inversion is located in the X chromosome, detection is either by the absence of half the males, or if the inversion itself is marked by a recessive lethal (as in the C1B method devised by Muller for Drosophila melanogaster), by the absence of all the males.