Isoenzymes of alcohol (ADH), malate (MDH), glutamate (GDH) and isocitrate (IDH) dehydrogenases, and a fast migrating esterase (EST-l) were separated by disk electrophoresis from dry seed extracts of diploid, tetraploid, hexaploid and octaploid species or amphiploids belonging to the subtribe Triticinae. Only ADH and EST-l isoenzymes showed inter-species variation; the other dehydrogenases, which show stringent substrate specificities (‘critical’ enzymes), revealed the same pattern in all diploid and polyploid species. The qualitative zymogram studies showed that (1) the number of variant enzyme bands increased with the level of ploidy, (2) the amphiploid isoenzyme pattern was additive of the parental species, (3) enhancement in the number of bands was due to the presence of not only parental bands, but also hybrid bands formed by association between heteromonomers. Quantitative data were obtained by densitometry of the enzyme bands as well as spectrophotometric measurements of enzyme activity in crude extracts. Increase in the level of enzyme activity was observed with ploidy level. In spite of the evidence that all duplicate/triplicate genes are expressed, increased enzyme activity observed in the polyploid species was not proportional to the level of ploidy or expected gene dosage. On the basis of ADH and EST-l zymograms obtained in 2 × and 4 × wheat, probable zymograms for these enzymes in the B-genome donor to 4 × wheat were extrapolated. Neither Ae. speltoides nor Ae. bicornis showed the extrapolated ADH pattern. Amphiploids involving Ae. speltoides and Triticum monococcum or T. aegilopoides fully reproduced the EST-l zymogram of 4 × wheat, but not the ADH. Ae. bicornis × T. aegilopoides amphiploid showed an ADH zymogram similar to that of 4 × wheat, but the EST-l bands were different.

Two ecotypes have been described for Culex pipiens mosquitoes of the temperate zone: a human commensal type and a feral type, but their degree of evolutionary differentiation and taxonomic status are still unclear. The commensal form is characterized by life-history traits probably adaptive to underground man-made environments. This situation has sometimes been considered as an example of recent speciation although the existence of intermediate forms indicates that the balance between gene flow and disruptive selection should first be assessed. The present study was concerned with (1) the determination of biological traits involved in adaptation to commensalism, and (2) the pattern of gene flow within and between ecotypes in a restricted area. It was found that (1) significant differences in biological traits exist between mosquitoes from different habitats, (2) characteristics of the commensal type are not universal in mosquitoes from underground man-made habitats, (3) allozyme markers do not clearly differentiate ecotypes and (4) insecticide resistance genes, which reveal recent migration, occur in each ecotype. These results are discussed in the context of possible speciation due to commensalism.

The genetical and developmental aspects of six dumpy mutants of Drosophila melanogaster have been investigated. The mutants obm, lm and olv (possibly alleles), lv, lv1 and lvI (possibly alleles) were known to be lethal when homozygous. Previously the lethal effect has been treated as a uniform effect. However, the lethal stage is not the same for all homozygotes, being egg/larval (E/L) for the three lv alleles, egg (E) for olv, larval/larval ecdysis (L/L) for lm and E/L and larval (L) for obm. Not all heterozygous combinations are lethal, i.e. obm/lm and obm/lvI are not lethal. Phenotypically the lethal heterozygotes fall into two patterns: (i) combinations not involving the allele obm and (ii) combinations involving obm. In the former, the mutant with the developmentally later expression is ‘dominant’ to the mutant with the developmentally earlier expression. In the latter, the genotypes manifest different proportions of individuals at the lethal stages E, E/L and L. Previous observations suggested that the lethality of the homozygote obm/obm was associated with the presence of an independent lethal in the stock. Observations presented here suggest that the lethality is a function of the obm allele itself. Complementation between some of the lethal mutants is not in accordance with the general rule for dumpy that compounds manifest the traits they have in common.

Tipsy (symbol ti) is a fully penetrant recessive mutant in linkage group VII of the mouse. Homozygotes have a peculiar rabbit-like gait from the age of a week, followed soon after by a tendency for the fore-part of the body to sway from side to side, leading to a reeling locomotion with falling over in severely affected mice. There is marked variation in manifestation and some amelioration in older animals; both sexes are fertile.

Linkage relationships in group VII are discussed and tipsy is compared with other mutants showing locomotor instability.

Sublines carrying isolated polygenes determining body size, developed by selection and repeated backcrossing to the LG and SM strains of mice, were inbred by full-sib matings with concomitant selection to study the inheritance of body size, using birth, weaning (28-day) and 60-day body weights as indices.

Mean body weights in those sublines backcrossed to SM and selected for large body size were greater than in those selected for small body size, proving that the difference resulting from seven earlier generations of backcrossing and selection, although small, was genetic and could be fixed by inbreeding. The mean body weights of the sublines selected for small body size drifted upward despite downward selection, a phenomenon thought to be due to the pressure of natural selection outweighing that of artificial selection.

In the sublines developed from backcrosses to the LG strain, mice from lines selected for small body size attained a mean body weight greater than that of mice from lines selected for large body size and also than of the parental LG strain. These results were contrary to expectation and a genetic interpretation was offered.

The macronuclei of Stentor coeruleus were isolated on a discontinuous sucrose gradient and their DNA was purified by conventional methods. The GC content was 32 mole%. The DNA banded as a single peak on analytical ultracentrifugation at 1·691 g/cm3. The molecular weight of the DNA was 5 × 106 to 4 × 107 daltons. Genome size determined by DNA–DNA reassociation kinetics was 6 × 1010 daltons. The macronuclear genome was mostly simple, about 85% being made of non-repetitive sequences.

Eight species of Tribolium and the related species Alphitobius diaperinus have been microdensitometrically analysed by measuring the nuclear content (1C value) of their Feuigenstained spermatids. The range of mean genome sizes goes from 0·157 pg in T. audax to 0·388 pg in T. brevicornis, including five significantly different groups of values. Also, in ail but one species of Tribolium significant intraspecific heterogeneity of genome size was found. The resemblances in genome size are not generally correlated with genetic homologies among species, but there is a highly significant correlation between genome size and spermatid size.

Lethal and semilethal t-haplotypes in the mouse are polymorphic in wild populations, where they are presumably maintained by transmission distortion from males, which transmit the aberrant chromosome to over 95% of progeny. We report here measurements of transmission ratio that show an unexpectedly strong effect of background genotype, specifically genes on the homologous chromosome, on the degree of transmission distortion of t-haplotypes. We also provide additional evidence that within t-haplotypes two separable elements co-operate to control transmission distortion, and that the system is thus closely analogous to segregation distortion in Drosophila, as has been previously proposed by Gluecksohn-Waelsch & Erickson (1970), Demin, Safronova & Lapkina (1978), and Styrna & Klein (1982).

We studied the evolutionary dynamics of extranuclear genes taking into account simple kinds of selection, two modes of inheritance and the multiplicity of genomes within a cell. Particular attention was paid to the accumulation of advantageous or deleterious mutations in an extranuclear genome. Within-generation drift due to multiplicity of genome and non-Mendelian segregation promotes the fixation of advantageous mutations and prevents deleterious mutations from accumulating. We show also that the extent of paternal contribution makes little difference in the rate, but, in contrast, the configuration of the genome and the mode of transmission both makes a large difference. These results are compatible with what is known about extranuclear genomes.

Despite the increasing number of studies on the magnitude of Ne/N ratios, much remains unknown about the effects of demographic and environmental variables on Ne/N. We determined Ne/N for seven population size treatments, ranging from N = 2 to N = 960, in the red flour beetle Tribolium castaneum. Ne/N decreased with increasing N, as evidenced by a significant negative relationship between log N and Ne/N. Our results are consistent with other published data on the relationship between Ne/N and N. Effective population sizes in large populations may be much smaller than previously recognized. These results have important implications for conservation and evolutionary biology.

Brassica juncea Coss (2n = 36) is a naturally occurring allotetraploid. In the progenies of F1 hybrids of its constituent parents B. campestris sub.sp. oleifera var. toria × B. nigra and B. campestris sub.sp. japonica × B. nigra, the majority of the plants were parthenogenetic homozygous amphidiploids like B. juncea whereas a few differed in morphological and physiological characteristics. The latter, presumed to have arisen partheno-genetically, were suspected to be homozygous for chromosomes changed by allosyndetic recombination. One of these derived plants with curley leaves was crossed first with one of the homozygous amphidiploids and secondly with B. c. sub.sp. oleifera var. toria. Sporocytes of the two hybrids were studied at meiosis. The presence of one or two quadrivalents in the first hybrid and two trivalents in the second suggested that allosyndetic recombination had occurred in the 18-chromosome hybrid. The progeny was presumed to have arisen through pseudo-diploid parthenogenesis and this in association with allosyndetic recombination may provide a means of breeding higher yielding genotypes.

The stimulation of in vitro tRNA aminoacylation by post-microsomal supernatant enzymes isolated from Abnormal Abdomen (A53g) adult flies is a function of the residual genome of these flies rather than of the major mutant gene, A53g. Genes controlling this stimulation are located on the X chromosome as well as on the autosomes. These observations are discussed in terms of the phenotypic effect of the major mutant gene in response to changes in protein synthesis which are under the control of modifier genes responsible for aberrant genetic translation mechanisms.

Time until fixation of a mutant that occurs in one copy of a multigene family was investigated from the standpoint of population genetics. Because of the complexity of the double process of random drift (on the chromosome and in the population), an approximate method based on the rate of steady decay of genetic variability is applied. The simple model of gene conversion with constant gene family size is also used. The expectation based on the approximate method is shown to be valid by extensive Monte Carlo simulations, and the results are useful for understanding the mechanisms of turnover of multigene families, when comparison is available between closely related species.

Manganese and cobalt are capable of inducing ρ− mutations* in non-growing cells of Saccharomyces cerevisiae, but their mutagenic action is much stronger in growing cells. At a given concentration cobalt and manganese can be either strongly mutagenic or non-mutagenic, depending on the cell density.

Most of the ρ− mutants induced with manganese and a considerable proportion of those induced with cobalt are suppressive and/or transmit drug resistance markers, so they must still carry mitochondrial DNA. Cobalt can decrease suppressiveness with low efficiency and eliminate drug resistance markers from established ρ− clones.

We have described a new unstable mutant of the vestigial locus isolated from a natural population. From this mutant, vestigialalmost (vgal), wild-type (vgal+), and extreme (vgext), alleles arose spontaneously. The molecular analysis of vgal shows that the mutation is due to a 1874 bp hobo element inserted in a vestigial intron. Two distinct kinds of events lead a wild-type phenotype. Three independent vgal+ alleles result from an excision of the hobo element and two other vgal+ alleles have further deletions of hobo sequence. The sequence of one of them shows a 1516 bp hobo insertion at the same place and in the same orientation as the 1874 bp insertion. In the vgext alleles, we found a 5′ or 3′ variably sized deletion of vg sequences. One of them, which has been cloned and sequenced, has a deletion finishing exactly at the left terminal repeat′ hobo element. The genetic implications of these different genetic structures are discussed.