| First Author | Lyon MF | Year | 1994 |
| Journal | Mouse Genome | Volume | 92 |
| Issue | 3 | Pages | 503 |
| Mgi Jnum | J:27499 | Mgi Id | MGI:74988 |
| Citation | Lyon MF, et al. (1994) Webbed toes as an effect of an allele of belted, btH. Mouse Genome 92(3):503 |
| abstractText | Research News: Full text of Mouse Genome: 2. Webbed toes as an effect of an allele of belted, btH. In a stock carrying the t-haplotype th20 and the brachyury allele, T21H, and of wild-type coat colour, animals with a white sash, phenotypically resembling homozygous belted, bt/bt, were found among the offspring of two trio matings with a common ancestor. One trio produced one sashed mouse out of 25, and the other 16 sashed among 60 young. This is consistent with segregation of a recessive gene, with both males and three of the four females of the crosses being heterozygotes. Outcrosses of sashed animals to wild-type gave 0/21 sashed, whereas matings of sash x sash gave 26 young all sashed. An allelism test of sashed with belted, by crosses of sashed with bt/bt gave 29 young, all with typical white belts. It was therefore concluded that the sash was due to an autosomal recessive gene with good penetrance, and allelic with belted, bt. It was given the allele symbol btH. When the affected animals were first found no anomalies were noted in the feet. However, after a few generations two belted animals, in separate crosses, were noted to have apparently fused toes. Outcrosses of these animals to normal-toed non-belted mice gave 68 young, all non-belted and with normal toes. Matings of homozygous btH/btH animals with fused toes to each other gave 64 out of 71 mice with fused or webbed toes. Thus, the toe anomaly behaved as though due to a recessive gene with incomplete penetrance. However, among the offspring of pairs segregating for btH only btH/btH mice seemed to be affected. In crosses of +/btH x btH/btHh, 36 of 42 btH/btH young and 0 of 50 +/btH young showed abnormal toes. Thus, the toe anomaly could be due to a gene closely linked to btH, or could be a pleiotropic effect of this gene. The data are not adequate to distinguish between these possibilities, but the latter seems more probable. It seems highly improbable that a linked gene should have mutated in the btH stock within only a few generations from the discovery of the gene. A more plausible explanation is that there should have been some change in the genetic background of the stock which favoured the expression of the toe anomaly in the btH/btH animals. A point in support of this is that occasional animals have been found in the related TFH/H inbred strain, and in other stocks also related to TFH/H, which have shown white spotting in the belt region together with webbed or fused toes. In no case has the phenotype shown either good dominant or recessive inheritance. However, the occurrence of these sporadic animals is consistent with there being factors present in these stocks which favour appearance of such a toe anomaly. The expression of the defect is variable. Any number of feet from one to four may be affected, and the degree of effect may vary from apparent fusion of two, or three digits, usually digits 2 and 3, to partial webbing of two digits. Alizarin preparations of the skeleton of 11 animals showed that the defect was one of soft tissue only. The phalangeal bones were normal in all animals. Thus, the anomaly is more correctly described as webbing of the toes rather than fusion. There is no evidence whether the original allele of belted, bt, is also susceptible to this type of toe anomaly (Lyon and K Whitehill). |
