Cytological observations of deletions in pachytene stages of oogenesis and spermatogenesis in the mouse.

Cytological examination of pachytene stages of oogenesis and spermatogenesis revealed the presence of diagnositc loops in cells heterozygous for each one of six radiation induced lethal albino alleles in the mouse. Such loops were never found in any of the normal sibs or other controls. Such evidence supports the contention that all six of these mutations are deletions as indicated previously for five of them by complementation tests. An incidental finding was that of a pleiomorphic region on a medium sized pachytene bivalent in both sexes. This was not restricted to mutant cells but was also found in control cells. Whereas the pachytene deletion loops characterize lethal albino allele carriers, the observation of the pleiomorphic region reveals an apparently normal cytological phenomenon in the mouse, the significance of which remains to be determined.