Table 1.
Mutants isolated
| Mutant | Mutant/total embryos, % | Map position
|
% Penetrance (homozygotes, n) | ||
|---|---|---|---|---|---|
| Chromosome | Closet marker (cM), no. nonrecombinants | Interval, cM | |||
| 25 | 50/292, 17.1 | — | — | — | — |
| 105, opm | 84/364, 23.1 | 12 | D12Mit69 (28.0), 68* | 6.0–28.0 | 88 (8) |
| 118, opb2 | 39/140, 27.9 | 1 | D1Mit318 (18.5), 82 | 17.0–20.2 | 94 (18) |
| bnb | 89/361, 24.7 | 6 | D6Mit159 (7.0), 61 | 3.0–15.5 | 100 (8) |
| wsnp | 126/509, 24.8 | 16 | D16Mit59 (27.8), 39 | 21.5–32.0 | 100 (5) |
The second column shows the total number of phenotypically mutant embryos per total embryos in mutant-containing litters observed. Closest marker is the marker that showed no recombination with the mutation (except for 105, see*) [Mouse Genome Database (MGD) map position]. No. nonrecombinants, number of independent meiotic products in which the chromosomes carried both the mutation and the closest marker, including data from both heterozygous adult carriers and homozygous mutant embryos. Interval includes the gene responsible for the phenotype, defined by flanking markers that recombine with the mutation (MGD map position). The last column shows direct measurement of penetrance. For each line, all the embryos from several litters were typed and embryos that were not recombinant between flanking markers were scored. Penetrance was defined as the number of homozygous embryos that showed the mutant phenotype out of the total number of homozygous embryos in these litters. The high penetrance of opb2, bnb, and wsnp measured directly is consistent with the 25% mutant embryos seen in mutant litters in these lines (column 2). For opb2, bnb, and wsnp, only embryos that were homozygous for the region showed the mutant phenotype. The opm mutation is not completely penetrant: 7/8 embryos homozygous for the region of chromosomes 12 were exencephalic. In addition, some exencephalic embryos in line 105 litters were not homozygous for opm (see *).
There are exencephalic embryos in line 105 that are not homozygous for the chromosome 12 opm mutation, apparently because of other mutations induced in the line. We observed that this marker was linked to the opm mutation in 68/88 independent meiotic products genotyped; some of the cases where linkage was not observed are presumably recombinants, whereas others represent embryos that were presumably exencephalic because of mutations at other genomic loci.