Several ribosomal RNA (rRNA) genes from D. busckii were cloned and characterized. The prominent repeat classes have lengths of 12·8 and 13·6 kb and lack 28S introns. rRNA genes were cloned containing 28S insertions which exhibit heterogeneity in size and sequence. The non-transcribed spacer (NTS) contains two regions composed of different repeated sequences that exhibit pronounced instability in HB 101. NTS region II, centrally located within the NTS, contains predominately 11 or 16 HincII generated 160 bp repeats. NTS region III, next to the 18S gene, contains repeats that are variable in number, and are either heterogeneous in length or are dispersed within unique sequences. The organization and composition of the rRNA gene NTS of D. busckii is different in comparison to the NTSs of other drosophilids. In addition, the pronounced instability of two different NTS regions is unique in comparison to all other cloned rRNA genes.

The phylogenetic relationships of the eight species of the Drosophila melanogaster subgroup are examined on the basis of genetic variation at 33 putative enzyme loci. Values of Nei's genetic distance (ds) range from 0·28 to 1·74. D. sechellia appears closer to D. simulans than to D. mauritiana, the two former being the most closely related. D. orena is quite distantly related to D. erecta (ds = 1). Genetic differentiation supports the existence of three main lineages within the melanogaster subgroup and the yakuba-teissieri pair appears to be closer to the melanogaster lineage than to the erecta-orena one. Inferences of the times of species divergence from allozyme data are made and their agreement to other estimates is discussed.

Linkage disequilibrium between five polymorphic enzymic loci of the third chromosome (Esterase-6, Phosphoglucomutase, Esterase-C, Aldehyde Oxidase and Acid Phosphatase) was studied in experimental populations of Drosophila simulans. Gametic data were obtained by mating sampled males with homozygous females at the five loci. Four cage populations were initiated with flies caught from natural populations. Extensive linkage disequilibrium was detected after 25 or 34 generations. The effective size of these populations was estimated about 400. Monte-Carlo simulations were performed in order to determine whether the observed disequilibria could be due to genetic drift. The observed probability distribution of the experimental values of r (the gametic correlation coefficient) was consistent with the distribution expected under random genetic drift. Our results are thus in accordance with the neutralist hypothesis.

Using a mouse Y chromosomal repetitive sequence that differentiates between the Mus musculus musculus type Y chromosome and the M. m. domesticus type Y chromosome, we studied the Y chromosome in M. m. molossinus, M. m. castaneus and M. m. subspecies specimens recently trapped in Japan, Taiwan and China as well as Asian mice maintained at the Jackson Laboratory and Litton Bionetics. Here we report that the M. m. musculus type Y chromosome predominates in Asian house mice and that Japanese mice maintained at some laboratories may not represent typical M. m. molossinus.

Wild house mice, Mus musculus, were bred (a) at 3 °C (‘Eskimo’) and (b) at 23 °C. Mice of the ninth generation bred at 23°C were transferred to the cold environment. Their young, and Eskimo of the same (tenth) generation, were mated to give the four possible types of pairs: controls; the two reciprocal hybrid pairings; and Eskimo. In the resulting (eleventh) generation there were therefore two hybrid classes, genetically identical but with different parentage. The growth and reproduction of the eleventh generation were studied. At all ages from birth, mice with Eskimo mothers were heavier than those with control mothers. They were also better breeders: (1) they matured earlier; (2) their litters were larger; (3) the mortality of their young in the nest was lower. In one feature there was heterosis: of the four classes, the hybrids with Eskimo mothers produced the largest litters. These and previous findings suggest rapid selection, in the cold, for changes in growth, reproductive physiology and other aspects of metabolism. The cold-adapted mice of a given generation differed from the controls partly as a result of favourable parental effects, which acted in conjunction with genetical differences. It is hypothesized that the ecological versatility of Mus musculus depends partly on the presence, in each population, of alternative genotypes which allow rapid adaptation to new conditions.

Testis size was investigated in two inbred strains of mice, BALB/c/Ola and CBA/Gr, at different ages. BALB/c mice were found to have the larger testes from day 14 of embryonic development onwards. Body weights of the two strains differed to a lesser extent. The differences in testis weights were analysed post-natally at 2, 4, 6 and 8 weeks in the two strains, F1s, F2s and backcrosses. Testis size was found to be affected by the origin of the Y chromosome, the X chromosome, the autosomes (and/or pseudoautosomal regions) and by maternal factors. At 8 weeks of age, the Y-chromosomal effect was at its strongest, and the X-chromosomal effect was at its weakest, while the maternal effect had vanished. It is postulated that non-Y-chromosomal factors which modify testis size may affect the gonads in both sexes. The possibility is discussed that loci affecting gonad size may be identical with testis-determining factors.

In C57BL/10 and the majority of other strains of mice, females have about 20-fold higher kidney histidine decarboxylase levels than males; in DBA/2 mice, however, HDC in females is only 3- to 4-fold higher than males. The low ratio HDC phenotype of DBA/2 animals is due to decreased sensitivity of the HDC gene complex to repression by testosterone in males. From conventional crosses and by the use of the BXD recombinant inbred lines we conclude that the C57BL/ 10: DBA/2 difference, in testosterone sensitivity of HDC, is due to an allelic difference in the regulatory gene Hdc-a of the HDC gene complex, [Hdc], on chromosome 2; DBA/2 contains a third allele of this gene, Hdc-ad.

Irradiation has been employed successfully to increase the reverse mutation rate at the agouti and dilute loci in the mouse. The dilute allele has previously been shown to be due to the insertion of an ecotropic-specific murine leukaemia virus in the vicinity of the dilute locus, and its instability to be due to the excision of the proviral sequence (Jenkins et al. 1981). Molecular analysis of the recovered radiation-induced revertant at the dilute locus indicated excision of all but approximately 500 bp of the proviral sequence. The proviral sequence remaining in the mouse genome hybridizes to a probe specific for the proviral long terminal repeat (LTR) sequence. Previous characterization of two spontaneous reverse dilute mutations indicated precise proviral excision of all but a single LTR, and suggests homologous recombination between the proviral LTR sequences as the mechanism of proviral excision (Hutchison, Copeland & Jenkins 1984). The present results indicate that radiation and increases the reverse mutation rate at the dilute locus acts by a similar mechanism, and suggest that mutagenic treatment may be employed to produce genetic variants of interest.

We have utilized isoelectrofocusing two-dimensional polyacrylamide gel electrophoresis (IEF-ID-PAGE) to determine the frequency of variant proteins detected in mouse testes, and to examine an inbred strain with spermatogenic abnormalities. The observed frequency of variants, 4·2 ± 1·0%, is comparable to results reported for liver. A variant for a protein, identified as tubulin by immunoblotting, was observed in an inbred strain (PL/J) which has defective spermatogenesis, but was also observed in another inbred strain without spermatogenic defects. The gene symbol Tbn is proposed for this β-tubulin locus.

The influence of mutations in chromosome 17 upon the segregation of the metacentric and acrocentric homologues in the progeny of female mice heterozygous for Robertsonian translocations Rb(8.17)11em and Rb(16.17)7Bnr was studied. Genetic analysis indicated that the portion of non-Rb (normal karyotype) progeny from mothers heterozygous for mutations tf, qk, t12 was weakly different from the 50% Mendelian expected level (55–57%). Introduction of mutations T, FuKi, Fu, t6 into the female genotype caused a stronger segregation distortion and an increase in the portion of progeny with normal karyotype (63–67%). From the data on embryonic mortality and cytogenetic observations it is concluded that a distortion of equal transmission arises before M II of meiosis. Consequently, the preferential distribution of the metacentric chromosome to the polar body during the first meiotic division is relevant to the observed segregation distortion.

An animal with low erythrocyte triose phosphate isomerase (TPI) activity was found amongst mice trapped on a farm in Leicestershire. The low TPI activity was caused by the segregation of a single co-dominant gene which also affected the Km for glyceraldehyde-3-phosphate and heat stability of the enzyme. We designate the gene Tpi-1, the structural locus for TPI, with the a allele in the common inbred strains and the b allele derived from the wild-caught mouse. Tpi-1 was known to be on chromosome 6 by somatic cell techniques and, as shown in a preliminary report (Peters & Bulfield, 1984), we have confirmed and extended this finding using three chromosome-6 marker genes giving the order: Sig-28-Lc-11-Miwh-16-Tpi-1.

An estimator is proposed for the parameter C = 4Nc. where N is the population size and c is the recombination rate. The estimator is appropriate for use with sequence or restriction site data from random samples from within populations. Properties of the estimator are investigated for an infinite-sites neutral model using Monte Carlo simulations. The median and mode of the distribution of the estimator are close to the true value for all parameter values examined, but large data sets are required to obtain reliable estimates.

Genet. Res., Camb. (1987), 50, pp. 17–21

Heterogeneity of human haptoglobin α chains detected by two-dimensional gel electrophoresis

The running title for this article should have been Human plasma haptoglobin α chain heterogeneity

Genet. Res., Camb. (1987), 50, pp. 63–68

Additive variance and average effect with partial selfing

(1) The second line of Table 1 should read