We have extended previous algebraic analyses of aberrant segregation at the gray locus of Sordaria fimicola (Whitehouse, 1965; Emerson, 1966; Fincham, Hill & Reeve, 1980) to the more complex situation where aberrant segregations are detected in three factor crosses involving two flanking markers. This algebra has been applied to seven gray alleles which have been extensively characterized for their pattern of gene conversion and postmeiotic segregation by Kitani & Olive (1967). It is based on seven major types of aberrant segregation which can be distinguished in the presence of flanking markers spanning the converting site, and allows us to use up to six parameters to describe hDNA formation and mismatch repair. We present solutions which predict a spectrum of aberrant segregation fitting the experimental data at the P > 0·05 level for six of the seven alleles tested. They are consistent with the following properties of hDNA at the gray locus: (1) the single stranded DNA transferred during hDNA formation has always the same chemical polarity. (2) hDNA is mostly, if not entirely, symmetric, and its probability of formation is constant over the whole gene. (3) Disparity in aberrant segregation is mostly, if not entirely due to disparity in mismatch repair.

The often remarkable similarity in structural gene products among related species has led to the hypothesis that species differences may reside largely in changes at regulatory gene loci. This hypothesis assumes that groups capable of speciating have allelic variation at regulatory loci in their natural populations. We have undertaken an analysis of the mode of regulation of the esterase 6 (Est 6) locus in Drosophila melanogaster to determine the nature and extent of regulatory gene variation in natural populations. Analyses of esterase 6 (EST 6) activity among strains carrying the same thermostability variants reveal that significant, specific-activity differences are present. Reciprocal crosses between lines having high and low EST 6 activity show that loci other than the Est 6 structural gene influence EST 6 activity. Analyses of male hybrids from crosses between D. melanogaster and simulans indicate that the X chromosome of these flies affects the expression of the Est 6 locus, resulting in unequal levels of enzyme activity from the two alleles. The effect is sex and tissue specific. Female hybrids carrying the X chromosomes of both species exhibit equal expression of the two Est 6 alleles. We have determined whether natural populations are polymorphic for X chromosomes which affect EST 6 activity by extracting single X chromosomes from wild-collected males and placing these chromosomes in identical genetic backgrounds. Stocks which are otherwise genetically identical but carry independently derived X chromosomes show significant differences in the activity of EST 6. These data suggest that regulatory loci may be commonly polymorphic in natural populations.

The reversible integration of a plasmid into a phage genome via int-mediated recombination permits rapid and facile analysis of plasmid genes. Seventy-six independent mutants in the β-lactamase (bla) gene have been isolated and genetically mapped. The end points of deletions generated by partial digestion with restriction enzymes have been identified and this, together with the assignment of some nonsense mutations to specific amino acid residues, allows alignment of the genetic map with the DNA sequence.

The insertion of a high-copy-number plasmid into a lambdoid phage chromosome which lacks a functional repressor gene confers on the hybrid ‘phasmid’ the capacity to grow on an immune lysogen. This was found to be due to titration of repressor because of plasmid replication. We have exploited this property in order to isolate mutants that affect plasmid replication. These mutants have been mapped in a region that was previously characterized as necessary for plasmid replication and incompatibility properties. Some of the mutations could revert at frequencies characteristic of single-base-pair change mutations.

Linear functions of Nei's genetic-distance statistic are calculated frequently in the literature of population genetics. Variance estimates for these linear functions are either not presented or incorrectly calculated. Part of the problem stems from the common assumption that distance statistics are independent random variables. This assumption is not generally correct. We describe methods for estimating the variance of linear combinations of genetic-distance statistics. We also suggest a method for constructing confidence intervals on genetic-distance statistics when these values are small (< 0·10) and their distribution deviates substantially from normal.

The suppressor of sable [su(s)2] restores the function of vermilion (v), purple (pr) and speck (sp) as well as sable (s) in Drosophila melanogaster. In this report various alleles of su(s) are compared for their relative effectiveness on three target mutations, v, pr and sp. Three criteria for suppression of pr and v were employed: visible phenotype, eye pigment levels (drosopterins and xanthommatin) and enzyme levels (sepiapterin synthase and tryptophan oxygenase). For sp only the visible phenotype was examined. By all three criteria pr was found to be more easily suppressed than v; v and sp were comparable. By use of pr with various alleles of su(s) either homozygously or in heterozygous combination with su(s)+, the extent of suppression of pr can be best demonstrated by observing the levels of sepiapterin synthase; normal levels of drosopterins were found in females when sepiapterin synthase was only 20% of normal. On the other hand, the extent of suppression of v is best demonstrated by the amount of xanthommatin eye pigment, because even the suppressed vermilion fly has < 10% of wild-type activity of tryptophan oxygenase when 1-day-old flies are examined; in older flies this enzyme can be as high as 50% of wild type. From these results we also demonstrated that su(s)2, and other alleles, are not recessive but, in heterozygous combination with su(s)+, cause marked suppression of pr and slight, but reproducible, suppression of v. The purple mutation, therefore, is particularly useful for studying the mechanism of suppression as well as for obtaining new mutant alleles of su(s).

Rifampicin-resistant mutants have been isolated from a Micromonospora sp. In one of these, rifampicin failed to inhibit [3H]UTP incorporation in osmotically shocked cells; consequently, resistance was probably not due to the alteration of rifampicin permeability. Parallel to the rifampicin resistance there was a substantial increase in the novobiocin sensitivity of the mutants. Rifampicin-sensitive revertants exhibited their original novobiocin sensitivity. At the same time there was no increase in their sensitivity towards coumermycin A1, an agent of related structure and activity. The possible mechanism for this pleiotropy is discussed.

Two aspects of sperm phenotype were examined for tw32/+ males of the inbred strains C3H and C57BL/6 (B6). Sperm from fertile C3H-tw32/+ males very rarely achieved fertilization in vitro, while sperm from congenie C3H-+/+ males had no such difficulties. The presence of tw32 had no effect on ability of B6 sperm to undergo fertilization in vitro. In fertile hybrid males produced from crosses of B6 and C3H strains, tw32 significantly reduced, but did not inhibit completely, the sperms' ability to fertilize in vitro. The presence of tw32 decreased by a factor of two the frequency of abnormal sperm heads in males of the B6 strain, but doubled the frequency in the C3H strain. Hybrid males resembled the C3H strain in this respect. The presence of T or T2J had no effect on the level of sperm abnormalities in any strain. These results emphasize the importance of genetic background in expression of t haplotypes in sperm, and suggest that tw32 can influence a range of sperm characteristics, by interacting with products of other loci.

Previous studies have shown that different alleles of the mouse X chromosomal controlling element locus, Xce, cause non-random X-chromosome inactivation as judged by variegation in the coats of female mice heterozygous for X-linked coat colour/structure genes, or Cattanach's translocation (Is (X; 7) Ct), or the relative activity of biochemical variants of the X-linked enzyme PGK. This paper presents evidence using the Kanda differential staining method on 6½ d.p.c. and 13½ d.p.c. female mouse embryos heterozygous for the marker X chromosome Is (X; 7) Ct and carrying different Xce alleles, that the Xce locus affects the randomness of X chromosome inactivation. Furthermore the fact that a marked Xce effect is demonstrable in female embryos as early as 6½ d.p.c. (i.e. very soon after the initial time of X-inactivation) is strong evidence that the Xce locus exerts its effect by causing primary non-random X-inactivation rather than by cell selection after initial random X-inactivation.

In the fungus Podospora anserina, mutations were selected which relieved the hypersensitivity to paromomycin caused by four suppressors assumed to be ribosomal ambiguity mutations (su1–31, su1–49, su1–60, su2–5). Our first purpose was to isolate new antisuppressor mutations and in fact a new antisuppressor gene, AS7 was uncovered. The AS7–1 mutant displays a pleiotropic phenotype and particularly a sporulation defect. On the other hand, a new su1 mutant was obtained which acts as a suppressor and also as an antisuppressor: it can specifically reduce the suppressor effect of certain su2 mutations. This property of some su1 and su2 mutations was already known. Apart from these mutations probably involved in the control of translational fidelity, six mutations conferring cross-resistance to paromomycin and neomycin were isolated. While four of them are localized in the Pm1 and Pm2 loci previously identified, the two others define a new gene which controls paromomycin and neomycin resistance, Pm3. Strains carrying the Pm3–1 allele are sensitive to temperature at the level of growth and sporulation. The three last mutations which were obtained confer no mutant phenotype when separated from the su1 background. They are closely linked to the su2 locus.

The pattern of response expected from fixation of mutant genes for quantitative traits in finite populations is investigated for a range of distributions of mutant gene effects. The eventual rate depends on the total variance of mutant effects per generation, but the initial rate and the variance of response is higher if the distribution of mutant effects has a large standard deviation or is leptokurtic. The difference between initial and eventual rates of response is greater with large population sizes.

For a range of assumptions, new mutants are unlikely to have much influence on response for 20 or so generations, but then may contribute substantially, such that no plateaux are obtained. However, information on the variance contributed by mutants is almost entirely on bristle number in Drosophila.

It is argued that the role of new mutants should be considered in designing breeding programmes, in particular in utilizing large populations.

The future value of mitochondrial DNA (mtDNA) sequence information to studies in population biology will depend in part on understanding of mtDNA transmission genetics both within cell lineages and between animal generations. A series of stochastic models has been constructed here based on various possibilities concerning this transmission. Several of the models generate predictions inconsistent with available data and, hence, their assumptions are provisionally rejected. Other models cannot yet be falsified. These latter models include assumptions that (1) mtDNA's are sorted through cellular lineages by random allocation to daughter cells in germ cell lineages; (2) the effective intracellular population sizes (nM's) of mtDNA's are small; and (3) sperm may (or may not) provide a low level ‘gene-flow’ bridge between otherwise isolated female lineages. It is hoped that the models have helped to identify and will stimulate further empirical study of various parameters likely to strongly influence mtDNA evolution. In particular, critical experiments or measurements are needed to determine the effective sizes of mtDNA populations in germ (and somatic) cells and to examine possible paternal contributions to zygote mtDNA composition.

The relationship between chromosome pairing and chromosome fragmentation has been studied in a gene controlled mutant of pearl millet (2n = 14). Premeiotic mitosis, premeiotic cell development and early prophase I are normal without any fragments, which first appear at pachytene. The extent of fragmentation varies from zero to very extreme with two discrete classes of plants, namely those with partial fragmentation and those with multiple fragmentation. A quantitative analysis of bivalent distribution and the distribution of AI bridges in desynaptic and fragmented cells show all of them to be nonrandom events. We suggest that in cells showing partial fragmentation the bridges and fragments result from U-type exchanges at pachytene. The reduced frequency of AII bridges indicates relatively low sister chromatid reunion at pachytene. In multiple fragmented plants numerous minute fragments were seen from pachytene. Despite these anomalies most PMCs complete meiosis but subsequently abort at the pollen grain stage. The mutant gene also causes disturbances in the sequence of meiotic development in the ear and in the synchronous development of PMCs within an anther. It has no effect on the tapetum or on the physiological development of the anther.

Two warfarin-resistant strains of the Norway rat, Rattus norvegicus, derived independently from wild populations in Wales and Scotland and both homozygous for a major gene at the warfarin-resistance locus, Rw, were found to differ in their hypoprothrombinaemic response to simultaneous dosage with warfarin and vitamin K. The Welsh strain gave a small response and the Scottish strain a large response. These two response levels segregated in Mendelian fashion in various crosses involving the two resistant strains and a third, non-resistant strain. This indicates that the Rw locus has a series of three multiple alleles, denoted Rww, Rws and Rw+. The results are discussed briefly in relation to biochemical, ecological and evolutionary aspects of warfarin resistance.

The distribution of sex-determinants in field populations of Musca domestica domestica L. was studied in 62 samples of flies collected at 53 sites (animal farms) between 1975 and 1981 in an area stretching North–South from Denmark (+ Iceland) to Sicily.

Karyological observations and genetic analyses demonstrated the existence of three types of population along a latitudinal cline. Populations of Northern Europe were of the standard type (XX females and XY males) with the Y chromosome determining sex. Those of Central and Southern Italy from sites below 100 m.a.s.l. (metres above sea level) were autosomal (XX females and males), sex in them being determined by autosomal sex-determinants for both femaleness and maleness. In the large intermediate zone the populations were mixed and had several karyotypes in both sexes. In this zone an altitudinal gradient was also observed, with autosomal determinants less common at higher altitudes. Genetic tests showed, in the autosomal and in the mixed populations, the presence of two autosomal male factors: M III, the most common, on autosome III and M II, on autosome II.

The gradient in sex determinants found in flies of Western Europe appears to be a dynamic phenomenon of relatively recent origin. Both climatic influence and selective pressure with insecticides have probably contributed towards the micro-evolution of populations with different sex-determinants in the houseflies of the area studied.

In(IL; IR)O Y348 is a pericentric inversion of linkage group I in N. crassa, with a breakpoint between fr and un-5 in the left arm and a breakpoint between ad-9 and nit-1 in the right arm. Approximate breakpoint location was found by tabulating crossovers between the rearrangement and markers in normal chromosome sequence. Inversion structure was verified by marked In O Y348 × In O Y348 crosses. Precise mapping of breakpoints was by duplication coverage. Inversions like O Y348 do not produce progeny with segmental chromosome duplications when crossed to normal sequence, but duplications were produced by crossing it to In(IL; IR)O Y323 (Barry & Leslie, 1982), another standard pericentric inversion, and to T(I → VI)NM103 (Turner, 1977), a translocation to a tip. Each of these rearrangements has a breakpoint within the inverted region of In O Y348. Two duplications from In O Y348 × In O Y323 were converted to normal chromosome sequence by double mitotic recombination. Besides expediting mapping, the technique of intercrossing rearrangements increasingly enables us to make segmental duplications exactly tailored for studying specific included genes.

During an extensive survey of drosophilid fauna in 1977, D. melanogaster was not collected in the Seychelles. However, a population was found in 1981 in Victoria city, suggesting a recent introduction of this species. With respect to allozyme frequencies or ethanol tolerance, this population is almost identical to European ones and very different from those living under a similar equatorial climate on the African continent. The frequencies of rare biochemical alleles perhaps suggested that this population was founded by a small number of flies, less than ten inseminated females. For various biometrical traits, the situation was not so clear: according to the trait considered, Seychellian flies are either intermediate between European and African populations or closer to the latter. These data suggest that a few flies, recently introduced from a temperate (European?) country, built up a big population which is now on the way to adapting itself to new tropical conditions. Such an involuntary experiment should afford a unique opportunity to distinguish the respective roles of drift and adaptation in the evolution of D. melanogaster geographic races.

The inheritance of cyanogenesis in Trifolium repens is governed by two unlinked genes, Ac/ac and Li/li which determine the presence/absence of cyanogenic glucosides and their hydrolysing enzyme linamarase respectively. Plants possessing dominant alleles at both loci release hydrogen cyanide when their leaves are damaged. Analysis of phenotype frequencies in ten natural populations showed a significant positive association in phenotypic state between these two loci within populations. Taking into account the results of a subsidiary study which showed no significant deviation from random mating in a natural population of T. repens, the most likely explanation for the observed association in phenotypic state is selection favouring the cyanogenic phenotype.

The production of MSHA+ (type-1 fimbriate) recombinants was observed in transductional crosses between different pairs of naturally occurring strains of Salmonella paratyphi B. MSHA+ recombinants were readily produced in transductions from MSHA+ donor strains to MSHA− (type-2 fimbriate or non-fimbriate) recipient strains, and less frequently between some pairs of MSHA− strains. The genetic evidence suggests that there are at least three different clones among MSHA− strains of S. paratyphi B. Relationships between the different strains and their possible origins are discussed.

Seven temperature-sensitive paralytic mutants were recovered from 4544 lines of ethylmethanesulphonate (EMS) treated autosomes in Drosophila melanogaster. These mutants have been designated temperature-induced paralytic (tip). The tip mutations belong to six different genes; four of these, tip-A, Tip-B, tip-C and tip-D are on the second chromosome while tip-E and tip-F are on the third chromosome. This paper describes the paralysing behaviour and genetic localization of the tip mutants.