Edward P. Evans

A Mouse Translocation Giving a Metacentric Marker Chromosome

The paper describes genetic and cytological studies of mice carrying a sub-metacentric chromosome, apparently formed by the combination of a medium-sized acrocentric chromosome with a small one having

A presumed deletion covering the W and Ph loci of the mouse

A new allele at the W -locus ( W 19 H ), found in a mutagenesis experiment in which females were irradiated, involves a presumed deletion. The deletion covers the Ph locus (which forms part of a gene complex with the W , Ph and Rw loci), and the locus of a recessive lethal 2 cM distal to W . It does not extend distally to the bl locus; nor does it involve the Rw locus, W 19 H / Rw compounds being viable and fertile. Thus, the length of the deletion is 2–7 cM. The non-involvement of Rw shows that, in the gene triplet Rw , W , Ph , Rw must lie proximal to W and Ph , whose relative position remains unknown. Heteozygotes for W 19 H are not anaemic, show only minimal white spotting and no pigment dilution; they thus resemble heterozygotes for the original W mutant allele and differ from W / Ph trans heterozygotes, which have extensive white spotting. In addition W 19 H heterozygotes may be small and runted, many are believed to die prenatally, and some in the nest. Their radiosensitivity is increased. Homozygotes die at the pre-implantation stage.

Genetic, physical, and phenotypic characterization of the Del(13)Svea36H mouse.

Abstract. The Del(13)Svea36H deletion was recovered from a radiation mutagenesis experiment and represents a valuable resource for investigating gene content and function at this region of mouse Chromosome (Chr) 13 and human Chr 6p21.3-23 and 6p25. In this paper we examine the physical extent of chromosome loss and construct an integrated genetic and radiation hybrid map of the deleted segment. We show that embryos which are homozygous for the deletion die at or before implantation and that heterozygotes are subviable, with a substantial proportion of carriers dying after mid-gestation but before weaning. The majority of viable carriers exhibit a variety of phenotypes including decreased size, eyes open at birth, corneal opacity, tail kinks, and craniofacial abnormalities. Both the heterozygous viability and the penetrance of the visible phenotypes vary with genetic background.

Mapping studies of the distal imprinting region of mouse chromosome 2.

The known limits of the distal imprinting region of mouse Chromosome (Chr) 2 are defined by the breakpoints of the translocations T(2;8)2Wa, (T2Wa), and T(2;16)28H, (T28H), in distal H3, and proximal H4 respectively. We have shown that T2Wa and T(2;4)1Go, (T1Go), which has a breakpoint in central H3 map close to a, non-agouti. Ada, adenosine deaminase, lies very near the proximal boundary and Ra, ragged, maps very close to the distal boundary, and is less than 0.2 cM from wasted, wst. From the current data Ada can be taken as the proximal, and Ra as the distal gene marker of the imprinting region on the linkage map. From consensus maps twenty three other markers, including fourteen genes, lie between Ada and Ra, some of which may be useful in investigations of imprinting. Of the markers included in the study reported here, four, Ada, ls, lethal spotting, Ra and wst lie or probably lie within the region but none display any evidence of imprinting. We suggest that recombination frequency is elevated in distal Chr 2, because in none of the crosses could the most closely linked marker be ordered in relation to the translocation breakpoint due to the high frequency of double crossovers.

Meiosis and fertility in XYY mice

Four XYY male mice that showed no evidence of somatic-cell mosaicism are described. All had much reduced testis weights and considerable impairment of spermatogenesis, so that few spermatocytes surviv

Localization of the Hprt locus by in situ hybridization and distribution of loci on the mouse X-chromosome.

The hypoxanthine phosphoribosyltransferase locus (Hprt) of the mouse has been localized by in situ hybridization to band XA6. Comparison of the distributions of known loci on the genetic and cytogenetic maps of the X-chromosome suggests some chiasma localization with a relatively high frequency of chiasmata in the F bands. In the A bands there appear to be fewer known loci than expected, but no evidence has been found so far of excessive chiasma formation.

T(In1;5)44H, a complex mouse chromosomal rearrangement with a phenotypic effect

A complex murine chromosomal rearrangement, T(In1;5)44H, was recovered after 5 Gy + 5 Gy (given 24 h apart) spermatogonial X-irradiation. T44H is a paracentric inversion of most of Chromosome (Chr) 1 (1A1-1H6), followed by splitting of the inverted segment through a reciprocal translocation with Chr 5, the latter breakpoints being in 1C2 and 5F. Linkage tests have shown that the probable order on Chr 1 is fz-ln-T44H with 2.4 +/- 2.4 crossover units between ln and T44H. On Chr 5 the probable order is W-T44H-go-bf with 7.1 +/- 4.9 crossover units between T44H and go. All heterozygotes show a marked dilution of coat colour. Heterozygotes of both sexes are fertile, producing small litters with a marked shortage of T44H carriers. The number of live embryos produced from female carriers is significantly lower than from males. Despite the complex nature of the rearrangement, complete chromosome pairing and chiasma formation occur regularly at meiosis. Depending on the strands involved, this leads to the production of either one or two dicentric chromatids per spermatocyte, and their disjunctional fate can be followed into metaphase II. Analysis of chromatid classes at this stage suggests reasons for both the high embryonic mortality and the shortage of liveborn T44H carriers.