| First Author | Evans EP | Year | 1995 |
| Journal | Mouse Genome | Volume | 93 |
| Issue | 2 | Pages | 424-6 |
| Mgi Jnum | J:28993 | Mgi Id | MGI:76531 |
| Citation | Evans EP (1995) Four further radiation-induced duplications. Mouse Genome 93(2):424-6 |
| abstractText | Full text of Mouse Genome contribution: Four further radiation-induced duplications . In addition to deletions a number of animals carrying what appear to be chromosomal duplications have been detected in our combined chemical-radiation mutagenesis studies. Here a further 4 are described. Dp(9)12H. This mutant arose in a female and was kept for testing on the basis of small size at birth and weaning and dark coat, characteristics of previously described deletions and duplications (Cattanach et al, Nature Genetics 3:56-61, 1993; Cattanach and Evans, CEC pp 93-100, 1994). The small size was regularly detected among the offspring at birth, approximately 50% of which survived to weaning. At this age the dark coat confirmed the classification. However, many of these animals appeared to have shorter heads than their normal sibs, eye size seemed smaller and a wild, erratic behaviour proved to be a further characteristic. The mutation could be transmitted through both sexes. Examination of G-banded chromosomes from the bone marrow showed an apparent duplication of the dark staining band E on Chr 9 and which increased the physical length by about 20%. All the 200 diakinesis/metaphase I stages scored from the testis of a male carrier contained 20 bivalents probably confirming that the extra chromatin was a duplication and not an insertion from another chromosome. Dp(1)13H. Arose as a female detected as small at birth and weaning, but most affected young of later generations could be seen to have milky abdomens (chylous ascites) at birth. No evidence of oedema was noted in adults, however. There was a shortage of mutants at birth (50%) and viability to weaning was reduced (30%). The mutation could be transmitted through both sexes. Cytogenetic examination showed over a 20% increase in the physical length of Chr 1 as a result of the duplication of bands Cl.1 to C4. At the diakinesis/metaphase I stages of meiosis in carrier males, 20 bivalents were regularly formed with that for Chr 1 frequently recognisable as being markedly unequal. Dp(9)14H. First observed in a female exhibiting small size at birth and weaning. These characteristics were inherited but from about weaning age shortened heads, some with twisted jaws and tooth mal-occlusion, were common features of the mutants. Birth weights were generally about 70% of normal, but there appeared to be a spread into the normal range, suggesting low penetrance. The latter conclusion could account for the low proportion of affected animals detected at birth (20%), especially as the subsequent viability was near normal, and litter size was not notably reduced. The mutation could be transmitted through both sexes. Karyotypic examination of cells from the bone marrow revealed a duplication of bands B, C and D in the mid-region of Chr 9 and which increased the physical length by about 20%. Together with Dp(9)12H (above) and Dp3H (Cattanach et al, Mouse Genome 92:352, 1994) three different duplications have now been observed in Chr 9 with a combined total length of approximately half the physical length of the chromosome. This would suggest that, as in the case of Chr 12 (Evans et al, Mouse Genome 93: 147-158, 1994) considerable triplication of segments of Chr 9 are compatible with viability and fertility. Dp(7)16H. Arose as a female displaying only small size at birth and weaning, a proportion of her young inherited these features but additionally a marginal darkening of the coat. The growth retardation was variable ranging around 80% of normal but a few were more extremely affected (50% normal size). Only about 30% of the progeny showed the size affect, there was little loss to weaning, and litter size was high. The shortage of affected young therefore suggests incomplete penetrance rather than low viability. Cytogenetic examination of mitotic cells from the bone marrow showed an aberrant Chr 7 in a form similar to a dicentric chromosome. In addition to a centromere and associated dark staining chromatin at the normal terminus, it had a constriction and equally dark staining chromatin at the distal terminus and also a short segment of pale staining chromatin beyond this. The total addition increased the physical length of the chromosome by about 25% but at this stage it is not possible to determine either the constitution or means of origin of the extra segment. No anaphase bridges were seen so the chromosome is not a functional dicentric, although it may have originated as a dicentric and the distal centromere may have been inactivated. It is of interest that a further identical mutant with the same karyotype has since appeared in another litter from the same father. Because of the unique nature of the aberrant chromosome, it is.. |
