| First Author | Cattanach BM | Year | 1974 |
| Journal | Mouse News Lett | Volume | 50 |
| Pages | 41-2 | Mgi Jnum | J:13647 |
| Mgi Id | MGI:61829 | Citation | Cattanach BM, et al. (1974) Crossover suppression in heterozygotes for tobacco mouse metacentric chromosomes. Mouse News Lett 50:41-2 |
| abstractText | Full text of MNL contribution: 5. Crossover suppression in heterozygotes for tobacco mouse metacentric Chromosomes. Crossing over has been found to be suppressed by several, but not all, of the 7 tobacco mouse metacentrics (Cattanach, MNL 49: 30; Lyon and Newport MNL 49: 30). New, or additional, data are as follows and generally support the concept of an association between crossover suppression and the relative abilities of the metacentrics to cause non-disjunction. T(4;6)2Bnr: Crosses of T2 +++/+ Sig Lc Mi<wh> males ++++/++++ males yielded the following progeny: T2 +++, 63; + Sig Lc Mi<wh>, 37; T2 Sig Lc Mi<wh>, 1; ++++, 0; T2 + Lc Mi<wh>, 8; + Sig ++, 9; T2 ++ Mi<wh>, 9; + Sig Lc +, 5. This gives recombinations values of T2 - Sig, 0.76 +/- 0.76%; Sig-Lc, 12.88 +/- 2.92%; Lc-Mi<wh>, 10.61 +/- 2.68%. This compares with Sig-Lc, 24% and Lc-Mi<wh>, 10% in equivalent normal crosses (Searle and Beechey, this MNL). Crossing over would appear to be suppressed proximally to LC in chromosome 6. The T2 results also contrast with those of equivalent crosses with the T(6;15)1 Ald metacentric which also carries chromosome 6. The following progeny were produced: TI +++, 44; + Sig Lc Mi<wh> 38; T1 + Lc Mi<wh>, 14; + Sig ++, 9; TI ++ Mi<wh>, 9 ; + Sig Lc +, 7. This gives recombination values of Tl - Sig, 0; Sig-Lc, 19.01 +/- 3.57%; Lc- Mi<wh>, 13.22 +/- 3.08%. This agrees fairly well with the TlAld-Lc Mi<wh> linkage data of Lyon and Hawkes (MNL 42:27). TlAld does not appear to suppress crossing over in chromosome 6. Structural heterozygosity is thus not the cause of the suppression brought about by T2Bnr. Lyon and Newport (MNL, 49: 30) have provided some evidence that T2Bnr also suppresses crossing over in chromosome 4. Additional backcrosses of T2 ++/+ bm males x + bm/+ bm females have yielded the following progeny; T2 ++, 26; + bm, 35; T2 bm, 3; +++, 11; T2 + m, 2;+ b +, 10. This gives recombination values of T3-b, 16.47 +/- 4.02%; b-m, 11.77 +/- 3.50%. These data support Lyon and NewportÕs evidence for crossover suppression proximally to b (typically 40% to outside marker) but not for the b-m region (typically 7-9%). T(5;15)3Bnr: Crosses of T3 ++/+ Rw go males x ++ go females have yielded the following progeny: T3 ++, 30; + Rw go, 32; T3 Rw go, 3; +++, 3; T3 + go, 10; + Rw +, 4; T3 Rw +, 1; ++ go, 0. This gives recombination values of T3-Rw, 8.43 +/- 3.05%; Rw-go, 18.07 +/- 4.22%. This data suggest the order in chromosome 5 is centromere-Rw-go. On this basis, crossing over is greatly suppressed proximally to Rw for the outer proximal marker lies about 34 units beyond Rw. Crossing over in the Rw-go region is greatly enhanced over the typical value of 8 units. Confirmation of the centromeric position has been obtained in linkage tests with T3Bnr and bf which is an outer marker approximately 13 units from go. Crosses of T3 +/+ bf males x + bf/+ bf females have yielded the following progeny; T3 +. 9; + bf, 23; T3 bf, 4; ++, 13. This gives a recombination value of 34.61 +/- 6.80% and establishes the order in chromosome 5 as centromere - Rw-go-bf. Linkage backcrosses between both T3Bnr and TlAld and uw show that uw is closely linked to the chromosome 15 centromere. Crossing over was not detected in either test among a total of 101 progeny. Linkage tests between T3 Bnr and bt are now in progress. T(8;12)5Bnr: Crosses of T5 ++/+ Os E<so> males x +++/+++ females have yielded the following progeny: T5 ++, 18; + 0s E<so>, 18; T5 0s E<so>, 8; +++, 9; T5 + E<so> 9; + 0s +, 7; T5 0s +, 2; ++ E<so> 0. This gives recombination values of T5-Os, 26.76 +/- 5.25%, and 0s-E<so>, 25.35 +/- 5.16%. These data provide little evidence that T5 Bnr causes any crossover suppression in chromosome 8 and it may be noted that T5 Bnr brings about relatively low frequencies of non-disjunction. T(9;14)6Bnr: Crosses of T6 ++/+ hr s males x + hr s/+ he s females have yielded the following progeny: T6 ++, 16; + hr s, 21 ; T6 hr s, 8; +++, 13; T6 + s, 6; + hr +, 3. This gives recombination values of T6-hr, 31 .34 +/- 5.67% and hr-s, 13.43 +/- 4.17%. These data support Lyon and NewportÕs (MNL 49:30) intercross data which showed little evidence of crossover suppression by T6Bnr in chromosome 14. Crosses of T6 +++/+ cw se tk males x + cw se tk/+ cw se tk females have to date produced the following progeny: T6 +++, 21; + cw se tk, 7; T6 cw se tk, 1; ++++, 0; T6 + se tk, 4; + cw ++, 7. This gives recombination values of T6-cw, 2.50 +/- 2.40%; cw-se, 27 Ð50 +/- 7.06%; se-tk, 0%. Recombination in cw-se and se-tk regions may thus prove to be less than that found by Falconer and Isaacson (1965) in chromosomally normal mice (38% and 6% respectively) and also less than observed by Lyon et al. (1968) in mice heterozygous for T163H (38% and 7%, respectively). It seems probable that T6Bnr is suppressing crossing over in chromosome 9, but, unlike the other metacentrics, this effect may be greater nearer the centre of the linkage group than in the vicinity of the centromere. T(16;17)7Bnr: Crosses of T7 ++/+ T tf males x ++ tf/++ tf females have yielded the following progeny: T7 ++, 47; + T tf; 49; T7 T tf, 0; +++, 1; T7 + tf , 0; + T +, 4; T7 T +, 1; ++ tf, 0. This gives recombination values of T7-T, 1.96 +/- 1.96% and T-ft, 5.88 +/- 2.32%. Together with Klein's (1971) linkage data on T7Bnr and H-2, these results provide little evidence that T7Bnr causes crossover suppression in chromosome 17. The relative non-disjunction frequencies for the chromosomes comprising each arm of TlBnr - T6Bnr are now being tested by genetical means. This should demonstrate to what extent, if any, non-disjunction is related to crossover-suppression with individual chromosomes. (Cattanach and Moseley) |
