Genetic tests for autosomal non-disjunction and chromosome loss in mice.

Two new genetic methods for detecting autosomal non-disjunction and chromosome loss in mice are described. Both methods involve the use of marker genes and Robertsonian translocations, the latter present only in tester parents, to detect events in chromosomally normal mice. With the Rb method, the tester parent carries one or more Robertsonian translocations heterozygously; with the MBH method the tester parent carries two Robertsonian translocations showing monobrachial homology. The high rates of meiotic non-disjunction in the tester mice provide gametes with specific extra or missing chromosomes which, at fertilization, can allow the survival of a proportion of the zygotes lacking or carrying an extra specific chromosome from tested chromosomally normal parents. The Rb method has been assessed for X-ray-induced chromosome 1 loss and non-disjunction in mature oocytes and also for such chromosome 1 loss from the maternal pronuclei of 1-cell zygotes. The MBH method has been assessed for X-ray-induced chromosome 1 loss in male postmeiotic cells and for non-disjunction in spermatocytes. Both methods proved effective in detecting chromosome 1 loss. A single case of the much rarer non-disjunctional event was also found. As applied, both methods compared favourably with the numerical sex chromosome anomaly (NSA) method and have considerable potential for further development.