Detection of triethylenemelamine-induced translocation heterozygotes in CD-1 mice: fertility and cytological methods.

A study was conducted to determine the extent to which translocation carriers can be missed in the heritable translocation test. CD-1 male mice were treated with the mutagen triethylenemelamine and bred to untreated females and male progeny were subjected to fertility and cytogenetic analyses. Fertility testing involved mating 1 male to 3 virgin females and subjecting the females to uterine analysis. The males were classified as having normal or reduced fertility according to the number of live implants produced by the females. The cytogenetic analysis involved scoring 25 primary spermatocytes per mouse for translocation multivalents. A total of 103 male progeny were analyzed. Evaluation of fertility and cytogenetic data confirmed the presence of 18 translocation heterozygotes among the male progeny. On the basis of fertility testing, 1 translocation heterozygote was classified as normal (false negative) based on the production of 11 or more live implants by at least 1 mated female. On the basis of cytogenetic analysis of 25 cells per mouse, 1 partially sterile male was classified as normal (false negative); however, analysis of additional cells showed that this mouse was a translocation heterozygote. The study demonstrates the importance of evaluating fertility and cytogenetic criteria to minimize the extent of misclassification in conducting a heritable translocation test.