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.

Denatured total proteins of two maize lines and their reciprocal F1 hybrids were analysed by two-dimensional electrophoresis. Quantitative (spot more or less intense) and qualitative (presence or absence of spots) differences exist between the lines, and correspond to 11% of the total reproducible spots. Non-additive effects on spot intensities were found in the hybrids, which display spots similar to the more intense parental spot for 11% of varying spots. This may correspond to dominance for regulatory systems controlling the protein amounts. Such interactions contrast with additivity classically described for enzymes or DNA.

rpoB is the structural gene for the β-subunit of E. coli RNA polymerase. The rpoB-3 allele confers resistance to the antibiotic rifampicin and is unusual in being dominant to the wild-type allele. We used the plasmid pZD23, a derivative of the broad host range conjugative plasmid RP4, to introduce the rpoB-3 allele into a range of bacterial species. Species belonging to the same family as E. coli (Enterobacter aerogenes, Citrobacter freundii, Hafnia alvei møller, Klebsiella pneumoniae, Salmonella typhimurium) expressed rpoB-3 to give a rifampicin resistant phenotype; this demonstrated heterospecific transcription. The transfer of pZD23 to the non-Enterobacteriaceae species Azotobacter vinelandii and Rhizobium leguminosarum did not result in rifampicin resistance. In the former case this was due to non-expression of the rpoB-3 resistance phenotype, in the latter case the dominant resistance phenotype had been lost from pZD23. Heterospecific transcription can be used as a criterion for the investigation of genetic relatedness between bacterial species.

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.

Six wheat/Agropyron intermedium addition lines are described on the basis of their phenotype and biochemical markers. An assessment of homoeology of each addition chromosome is made. Chromosome morphology, plant phenotype, isozyme and protein studies are compared with similar data for other wheat/alien addition lines and other members of the Triticeae. These comparisons give consistent results and it is concluded that addition lines L1, L2, L3, L4, L5 and L7 carry Agropyron chromosomes of homoeologous groups 7, 3, 1, 4, 5 and 6 respectively. This agrees with previously published work with one exception: the L5 chromosome belongs to homoeologous group 5 and not group 2 as proposed by Figueiras et al. (1986).

Mice were selected for growth from 3 to 9 weeks of age on a normal protein diet (N) containing 19·3% protein and a reduced protein diet (R) containing 5·1% protein. On each diet there were 3 high (H), 3 low (L) and 3 unselected control (C) lines. After 6 generations of selection, half of the mice in each line were tested on each diet. Responses were obtained when selecting for both increased and decreased growth on both diets. The realized heritabilities from within-family selection were 33 and 26% for the divergences on the normal and reduced protein diets, respectively. Consistent genotype-environment interactions were found when all lines were tested on both diets in generation 7. Performance on each protein level was best improved by selection on that protein level. Further, the correlated response was significantly less than the direct response when selecting on both diets. The estimates of the genetic correlation between growth on the two protein levels were low, rN = 0·16 from selection on the normal protein diet and rR = 0·51 from selection on the reduced protein diet. Selection resulted in a change in environmental sensitivity in the lines, dependent on the diet and direction of selection. The average of the divergences on the two diets was not dependent on the selection environment.

The P–M system of hybrid dysgenesis in Drosophila melanogaster is a syndrome of genetic abnormalities which appears in the progeny of crosses between strains different with regard to their possession of ‘P’ transposable elements. Cytotype is an extrachromosomal property which regulates the mobility of the P element. We report here data showing that a cytotype polymorphism previously observed in a natural population from North-Africa is stable over a period of 5 years. A potentially high rate of mutation is associated with this cytotype polymorphism. Explanations of the appearance of a cytotype polymorphism are proposed and the consequences for the genetic load induced by transposable elements are discussed.

The protein spots representing the haptoglobin α1F, α1S and α2 chains in two-dimensional gels of human plasma samples representative of the six common haptoglobin phenotypes were identified by comparing their position with those of purified haptoglobin and distinguished from other spots in the vicinity by comparison with plasma with undetectably low levels of haptoglobin. Silver staining indicated that the α1F chain was represented by one spot in subtypes 1F-1F, 1F-1S and 1F-2, the α1S chain by three spots in subtypes 1S-1S, 1F-1S and 1S-2 and the α2 chain by six spots in 1F-2, 1S-2 and 2–2

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.

Expression of X-linked genes for G6PD and GALA in interspecific hybrids between Microtus arvalis, M. subarvalis and M. kirgisorum voles was studied. Quantitative predominance of the enzyme activities of M. arvalis over G6PD activity of M. subarvalis and the GALA activity of M. kirgisorum in the female hybrids was shown. The definitive patterns of these enzyme activities was found on day 6·5 of embryonic development. Non-random inactivation of X-chromosomes derived from M. subarvalis and M. kirgisorum in the interspecific hybrids with M. arvalis is supposed to be the cause of the phenomenon observed. A hypothesis is proposed that there is a connection between the presence of large heterochromatin regions in the X-chromosomes derived from M. subarvalis or M. kirgisorum and the preferential inactivation of these in female hybrids with M. arvalis.

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.

Many inbred and isofemale lines derived from wild populations of Drosophila melanogaster were tested for gonadal dysgenic sterility, male recombination and snw secondary mutation. Among them, we have found strains whose dysgenic offspring show negligible sterility, and undetectable male recombination and snw mutation. They can be considered to be neutral strains in the strict sense. Such neutral strains appear to carry only defective P elements in their genomes. Taking the observations of Karess & Rubin (1984) into account, it is suggested that some defective P elements retain the function necessary for P cytotype. Cytotype determination mechanisms are discussed.

Sex determination in Drosophila depends on the ratio of X chromosomes to sets of autosomes (X:A). This chromosomal signal is used to regulate a few control genes whose state of activity selects either the male or the female sexual pathway. We have studied the structure and function of dsx (double sex) which appears to be the last regulatory gene on whose function the sexual pathway eventually depends. We have mutagenized the locus, varied the doses of dominant dsx-mutations and wildtype alleles, and combined different dsx-alleles with recessive mutations in other sex-determining genes, such as ix, tra-2 and tra.

The locus dsx harbours two genetic functions, dsxm to implement the male program, dsxf to implement the female program. We found that dsxm and dsxf can mutate independently although most mutations abolish both functions. We conclude that dsxm and dsxf each have their specific domain, but also share a large region of DNA that is essential for both functions. We present evidence that the dominant mutations correspond to a constitutive expression of the male-determining function dsxm, with the simultaneous abolishment of the female-determining function dsxf. This effect can be counteracted by two doses of expressed dsxf so that a female phenotype results. The products of one dose of expressed dsxm and one dose of expressed dsxf in the same cell appear to neutralize each other which leads to a null phenotype. The mutant combinations suggest that the product of dsxf requires the products of ix+, tra-2+ and tra+ to become functional.

The transmission ratio distortion seen in males heterozygous for a mouse t-complex has been explained on the basis of trans-acting distorter genes, having a harmful effect on a responder gene. The t-complex form of the responder is relatively resistant to these harmful effects and hence is preferentially transmitted. Animals homozygous for the t-complex responder would be expected to show equal transmission of the two homologous chromosomes, but this is not always so. Studies described in this paper have shown differences among complete t's in their transmission when opposite a constant responder carrying partial t-haplotype. In addition, the proximal partial haplotypes th49 and tw18, both derived from tw5 but of different lengths, behave differently when opposite a responder. The three central partial haplotypes, tlowH, tlow2H and tlow3H, also differ, in that tlow3H shows lower transmission than tlowH or tloW2H when opposite either wild-type, or another responder, or distorter genes. These results can be explained either on the basis of differences in the responder region of various haplotypes, including the possibility of varying numbers of copies of the relevant sequences, or on the basis of differences in cis-acting (as opposed to trans-acting) distorter genes.

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.

A method is developed for calculating the probability of establishment of an allele which is favoured in some places, but not others, in a large subdivided population. This method is quite general, and could be used to calculate the chance that any system which is linear near an absorbing boundary will move away from that boundary. The results are applied to a population distributed along one dimension. Only mutants which arise within a distance ∼ σ/ √2s of the region in which they are favoured stand an appreciable chance of establishment. The net chance of establishment of mutations distributed randomly across the habitat will be decreased by gene flow if selection against them is sufficiently strong. However, if the mutations are only weakly deleterious outside some limited region, gene flow may increase the net chance of establishment.

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 Lucilia cuprina (Wiedemann) females, non-segregation of compound fifth-chromosomes is correlated with non-disjunction of the X chromosomes. Approximately two-thirds of eggs which inherit both maternal compound elements are nullo-X, suggesting that meiotic pairing between X chromosomes and compound autosomes has occurred. There was no evidence for pairing of the compounds and the X or Y chromosome in males. A limited amount of data suggests that high non-segregation frequencies may occur in the offspring of putative X/X/X and X/O females. These results suggest the existence of non-homologous (distributive) pairing in L. cuprina females.

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.

The OTC gene coding for ornithine transcarbamylase is sex linked and subject to X inactivation in humans and mice. We have used a rat cDNA probe to localize OTC by in situ hybridization in marsupials and monotremes. The gene maps to an autosomal site in two distantly related marsupial species and in one monotreme (the platypus); the first demonstration that a gene X-linked in one mammalian species may be autosomal in another. Since the conservation of the mammalian X is thought to be a consequence of its isolation by the inactivation mechanism, we propose that an autosomal or pseudoautosomal segment containing OTC has been recruited into the inactivated region of the X rather recently in eutherian evolution while it remained autosomal, or was translocated to an autosome, in metatherian and prototherian mammals.