Breeding tests of wild house mice, trapped from an isolated population from Sanday in the Orkney Islands, have demonstrated the presence of a semilethal t-haplotype designated tw106. Microscopic examination of sperm and testes from a sterile male obtained from this population revealed the histological characteristics typical for homozygotes for semilethal t-haplotypes. This report is the first description of the recovery of a t-haplotype from an island population of wild mice.

The activity and thermostability of alcohol dehydrogenase (ADH) from 247 strains of Drosophila melanogaster were studied by spectrophotometric assay. The strains, in which second chromosomes had been made homozygous in a standard genetic background, were derived from five natural populations from diverse geographical and ecological sites. Evidence is presented that the majority of variation in ADH activity is attributable to the presence, in all five populations, of two electromorphs of the enzyme. However, some variation does exist between strains carrying the same electromorph, to some extent associated with variation hi body weight. Two strains showed atypical ADH activities. Variation in ADH thermostability was almost wholly attributable to the presence of two electromorphs; only two strains had enzymes with thermostabilities atypical of their electromorph. In the four strains with abnormal ADH properties the locus (loci) responsible map in the region of the Adh locus. Therelatively low level of heterogeneity within electrophoretic classes at this locus is discussed in view of recent findings at other enzyme loci in Drosophila.

The consequences of repeated backcrossing to a fixed parent are examined for haploid eukaryotes having a transitory diploid phase. The isogenicity attained in the absence of selected markers depends on the number of chromosomes and the total genetic map length, while the isogenicity of a chromosome carrying a selected marker increases more slowly and depends on the size of the chromosome. As inbreeding proceeds, the remaining non-isogenic material is not distributed evenly to all of the progeny. Instead, the majority of the progeny are completely isogenic with the fixed parent (with the exception of a region surrounding each selected marker), while the non-isogenic material is concentrated in a minority of the progeny. Even when the average isogenicity of the progeny and the fixed parent exceeds 99%, a significant proportion of the progeny will contain tracts of non-isogenic material which average several map units in length. Minor modifications enable these results to be applied to diploide. Examples show how to determine the degree of isogenicity produced by a given number of backcrosses in several specific situations.

Spatial and temporal differentiation in Gerris lacustris and G. odontogaster (Heteroptera, Gerridae) were studied in restricted areas, where one population of each species was subdivided into several subpopulations. The aim of the study was to relate genetic population parameters to ecological population structure studied by mark-recapture methods in the same pond systems. Marked differentiation between the subpopulations and significant enzyme allele frequency changes between subsequent generations were found at several loci. It is suggested that non-selective forces are a sufficient explanation for the observed differences.

pMO1111, a derivative of FP110 carrying a Tn1 insert, has been used to generate two plasmid primes carrying Pseudomonas aeruginosa chromosome. pMO1112 has been shown to carry the pro-82+ gene and pMO1113 carries argH+ and lys-12+. pMO1112 is considerably more stable than pMO1113 in a recA+ background.

The selection component analysis developed by Christiansen & Frydenberg (1973, 1976) is a method to study the components of natural selection and is based on an analysis of population samples which include mothers and their progeny (mother–offspring combinations). Because only one progeny per mother–offspring combination is analysed, gametic selection and the reproductive components of selection in males are poorly characterized. We investigated the information which can be gained by analysing all progeny in each combination and showed that analysis of entire litters enables detection of gametic selection. Testing and estimation procedures are derived for this purpose. Sexual selection in males and mate preferences remain poorly characterized because the only information about the reproductive components in males is contained in the sample of male gametes and is insufficient to reconstruct the breeding structure of the male population. The format and interpretation of a selection component analysis is presented which takes these results into account.

Internal sequences of Tn501(Hg) and Tn721(Tc) have been compared by hybridization. In spite of the difference in the resistance they code for, there is extensive homology between the two elements. This homology resides in the transposon-coded genes that are necessary for transposition and indicates that the elements are closely related.

A mathematical theory of population genetics accounting for the genes transmitted through mitochondria or chloroplasts has been studied. In the model it is assumed that a population consists of Nm males and Nf females, the genetic contribution from a male is β and that from a female 1 – β, and each cell line contains n effective copies of a gene in its cytoplasm. Assuming selective neutrality and an infinite alleles model, it is shown that the sum (H) of squares of allelic frequencies within an individual and the corresponding sum (Q) for the entire population are, at equilibrium, given by

and

where ρ = 2β(1−β), Ne = {β2/Nm+(1−β)2 / Nf}−1, λ is the number of somatic cell divisions in one generation, and v is the mutation rate per cell division. If the genes are transmitted entirely through the female the formulae reduce to Ĥ ≃ 1/(1 + 2nv) and Q^ ≃ 1/{1 + (2Neλ+ 2n)υ}. Non-equilibrium behaviours of H and Q^ are also studied in the case of a panmictic population. These results are extended to geographically structured models, and applied to existing experimental data.

The genetically determined oocyte-specific expression of glucose-phosphate isomerase activity in the mouse is first apparent at 6 to 7 days after birth, and occurs in XO as well as in XX oocytes. The regulator locus that controls oocyte-specific expression shows the same linkage relations as the structural gene, suggesting that both form part of a Gpi-1 gene complex.

The broad host-range non-conjugative IncQ plasmid RSF1010 was mobilised with 100% efficiency in membrane filter matings, both in E. coli K12 and P. aeruginosa PAO, by broad host-range conjugative IncP plasmids. No homology between RSF1010 and an IncP plasmid could be detected. In E. coli, IncIα and IncX plasmids, but not IncF, IncN or IncW plasmids, were also relatively efficient at mobilising RSF1010, while in P. aeruginosa, R91–5 (IncP-10) was highly efficient, but pMG5 (IncP-2) and FP2 (IncP-8) were very inefficient. IncP plasmids also mobilised several plasmids derived from RSF1010 for use as in vectors in in vitro recombination experiments very efficiently, and pSC101 quite efficiently: this reduces the level of biological containment possible with these plasmids.

The expression of X-linked phosphoglycerate kinase (PGK-1) in germ cells from embryos heterozygous for both PGK-1 and Searle's translocation T(X; 16) 16H was examined to investigate X chromosome activity during oogenesis. The Pgk-lb allele on the translocated X chromosome was the only allele active in somatic cells of all embryos and in germ cells from 12·5 d.p.c. embryos. However, an additional faint band representing Pgk-la activity was observed in germ cells from older embryos (13·5–18·5 d.p.c.) and neonates (1–2 d.p.p.). It is concluded that there is a period when only one X chromosome is active in early female germ cells and that reactivation of the inactive X chromosome takes place just prior to meiotic prophase.