Male meiotic behaviour and male and female litter size in mice with the T(2; 8)26H and T(1; 13)70H reciprocal translocations

Abstract

SUMMARYTwo reciprocal mouse translocations T(2; 8)26H and T(1; 13)70H, heterozygous in a Swiss random-bred background, show differences in the spectrum of multivalent configurations and in the segregational behaviour of these multivalent configurations. T26H/+ males mostly contained rings of four (R IV, 53·15%) and T70H/+ males chains of four, missing a chiasma in the shortest interstitial segment (C IV 11, 61·55%). The adjacent II frequency, estimated from metaphase II observations, was 8·47% in T26H/+ and 25·22% in T70H/+. Univalents of the shorter translocation chromosome of T70H are able to divide equationally at first anaphase. The hypothesis is advanced that time differences in chiasma terminalization during metaphase I-anaphase are important for explaining the difference in segregation observed between the two translocations. Translocation-caused non-disjunction is probably low in T26H/+ and 4–5% in T70H/+. Univalents involving T70H/+ are usually capable of co-orientation with the other chromosomes of the translocation complex. The summed percentages of adjacent II disjunction and non-disjunction caused by the translocations were estimated from the relative fertility scores of T/+ males and females versus +/+ males and females as 9·8% and 29·0% for T26H/+ and T70H/+ males, respectively, and 9·4% and 27·8% for T26H/+ females and T70H/+ females. For both translocations, the agreement between the various estimates is good. Chiasma frequencies are much higher in telomeric segments than in proximal segments containing centric heterochromatin.