The selection of chromosomally abnormal gametes was investigated in the Chinese hamster by direct chromosome analysis of meiotic cells and one-cell embryos obtained from crossing heterozygotes for two reciprocal translocations, T(1;3)7Idr and T(1;3)8Idr. Expected frequencies of male and female gametes with different chromosome constitutions were estimated by scoring of secondary meiotic metaphase (MII) cells in the translocation heterozygotes. The frequency of gametes with each karyotype that participated in fertilization was investigated in pronuclei from translocation heterozygotes in one-cell embryos obtained from crossing the heterozygotes with karyo typically normal animals. Compared with the expected frequencies from MII scoring, the frequencies of male pronuclei having some karyotypes in one-cell embryos decreased significantly. The karyotypes of male pronuclei showing a decreased frequency were commonly characterized by a deficiency of the long-arm segment of chromosome 1 (q13→qter) or by a deficiency of almost the whole arms of chromosome 3. On the other hand, the frequencies of female pronuclei with the same karyotypes were all consistent with those estimated from MII scoring. These results suggest that sperm nullisomic for certain segments of some chromosomes may fail to participate in fertilization.

Chromosome segregation and interchromosomal effects of reciprocal translocations at first meiotic division were investigated by chromosome analysis of meiotic cells from male Chinese hamsters heterozygous for two reciprocal translocations. We used six stocks heterozygous for two different translocations which were obtained by crosses between males and females homozygous or heterozygous for a different translocation. The frequency of second meiotic (MIl) cells from each segregational class of one quadrivalent in heterozygotes for two reciprocal translocations agreed with that of the same quadrivalent in heterozygotes for the single translocation. This indicates that the two quadrivalents in heterozygotes for two reciprocal translocations segregate independently. The mean frequency of hyperhaploid MIl cells from males heterozygous for two reciprocal translocations ranged from 7.1 to 15.4%. These cells were mostly derivatives from 3:1 disjunctions of the quadrivalents. The percentage of cells with extra chromosomes in translocation-unrelated groups was calculated at 0.10–0.25%. The frequency did not increase significantly as compared with that in karyotypically normal males, in which the mean frequency of hyperhaploid MIl cells was 0.39%. These findings revealed that reciprocal translocations do not have interchromosomal effects on meiotic division in male Chinese hamsters.