Laboratory mice carrying three pairs of Robertsonian translocations: establishment of a strain and analysis of meiotic segregation

Abstract

The evolution of a 2n = 34 combined Robertsonian translocation strain Rb(5.19)1Wh/(6.15)1Ald/(8.17)HEM is described. Homozygotes had three large ring translocation bivalents at M I and regular meiotic disjunction at M II. Male and female F_1· heterozygotes had similar frequencies of abnormal meiotic disjunction at M II, but aneuploid embryos were more frequent in (F₁♂ X NIH GP ♀) crosses (25.6%) than (F₁ ♀ X GP ♂) crosses (13.5%) at 10 days’ gestation. It could not be determined whether this discrepancy was genetic in origin or due to limitations in the techniques of M II analysis. Rb(5.19), as well as Rb(6.15) or (8.17), contributed to the aneuploidy, although previous M II analysis of singly heterozygous Rb(5.19)/+ males demonstrated comparatively regular meiotic disjunction. Trisomic embryos were not detected beyond 10 days in five (F₁ ♀ X GP ♂) crosses, suggesting that their survival in F₁ females is limited. The ratios of the different types of balanced embryos from the (F₁ X GP) crosses indicated random meiotic segregation of the three translocation chromosomes in triple heterozygotes. Analysis of complementary groups of balanced embryos from the same crosses also demonstrated lack of preferential segregation of the translocations; embryos with translocations and those with their corresponding homologous acrocentrics were equally frequent. Triploid embryos (3.3 %) were also detected in (F₁♂ X NIH GP ♀) crosses. The translocations and Y chromosome served as paternal markers, permitting its origin to be determined in two of three cases (dispermy). One growth-retarded triploid had a distinctive anomaly: failure of lens induction and lack of optic cup development. The combined strain provided a complex of markers for determining polyploidy mechanisms, as well as a common genetic background for comparing behavior of the three translocations at M I.

Aneuploid spermatocyte frequency in domestic sheep heterozygous for three Robertsonian translocations

“…This variation ranged from 5-81-2-33% in Ram B47/48 to 16-6-6-6% in Ram Bl 11/77, the mean level being 5-42% and is consistent with the individual variations in aneuploid metaphase II frequencies which have been found in all the single heterozygous rams studied so far (Chapman & Bruère, 1975;Long, 1978). This is similar to results from comparable studies on translocation-carrying mice (White & Tjio, 1967;Cattanach & Moseley, 1973;White, Crandall, Raveche & Tjio, 1978).…”

Cytogenetics and reproduction of sheep with multiple centric fusions (Robertsonian translocations)

“…The data presented here, when considered with previous reports (Bruère, 1974a(Bruère, , 1975Long, 1978b) (White, Crandall, Raveche & Tjio, 1978) the rapid combination of translocation does not significantly affect the random segregation process of the individual translocation hétérozygotes.…”

“…Pending the analysis of the triple hétérozygotes (t1t2t3) for levels of aneuploid secondary spermatocyte frequency, it would appear that although this may be shown to be higher than in single hétéro¬ zygotes (Chapman & Bruère, 1975) it does not lead to production of aneuploid zygotes. It should, however, be emphasized, that as in mice (White et al, 1978) the levels of aneuploidy in individual hétérozygotes need not necessarily correlate with those of the combined hétéro¬ zygotes, although in many examples an increase has been described Cattanach & Moseley, 1973).…”

Nondisjunction frequencies in Robertsonian heterozygotes from natural populations of the common shrew, <i>Sorex araneus</i> L.

“…These estimates will differ, as a large proportion of the pregnant females and their mates are double Robert sonian hcterozygotcs (table 1). The estimate in terms of heterozygous arm combinations would appear to be of more comparative value, but may be subject to error because (a) it is open to question whether the nondisjunction rate of multiple Robertsonian heterozygotes is that multiple of the nondisjunction rate of single Robertsonian hetcrozygotes (White et al [1978] and Bruere et al [1981] provide data for mice and sheep which suggest this is not necessarily the case), and (b) males may be more heterozygous than the minimum heterozygosity determined.…”