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 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.

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.

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 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.

Twenty t haplotypes were extracted from wild mice captured at several locations in Europe, Israel, North Africa, and South America. The haplotypes were designated tTuw1 through tTuw20. The H-2 haplotypes of the lines were defined using antisera and monoclonal antibodies specific for private antigenic determinants controlled by known H-2 alleles and by antisera produced using the new t lines as donors. The tTuw haplotypes fall into four groups according to the H-2 haplotype associated with them. Haplotypes tTuw10 through tTuw18 are associated with H-2W30, previously found to be linked with haplotypes of the tw1 group. Haplotypes tTuw1 through tTuw6 are associated with a new H-2 haplotype, H-2w36, characterized by the determinant H-2.107. Haplotypes tTuw7 through tTuw9 are associated with another new H-2 haplotype, H-2w37, characterized by determinants H-2.108 and H-2.111. And finally, haplotypes tTuw19 and tTuw20 are associated with yet another new H-2 haplotype, H-2w38, characterized by determinants H-2.33 and H-2.109. These findings suggest that the t polymorphism might be more extensive and more intricate than it was previously thought to be and that at least some of the t-associated H-2 haplotypes, and probably also the t haplotypes themselves, are related to one another in their origin.

We consider an age-structured population that is observed at times t = 0, 1, 2,…. It is assumed that for each t there is the same number of individuals of a particular sex and age group. Another assumption we make is that an offspring of a specified sex has at all times the same probability of having a parent of a particular age and sex. It is shown that the rate of substitution of neutral mutants is /L, where and L are respectively equal to the mean fraction of mutants among gametes succeeding in forming newborn individuals and the mean age of reproduction. This result also applies to monoecious populations. The substitution rate is also derived for advantageous mutants in a monoecious population. Once again, the mutation rate in the usual expression is replaced by /L. Implications of these results are discussed.

Evidence for close genetic linkage between the structural loci for serum albumin (Alb) and serum vitamin D binding protein (Gc) in chicken is presented. The results are based on a study of a single sire family comprising 36 informative offspring. No recombinants have been observed. It is concluded that this linkage in the chicken is homologous to the close linkage of the albumin and Gc loci reported in man and the horse. Thus, this linkage group has most probably been conserved for at least 300 million years.

The interpretation of gene conversion data from ordered eight-spored asci

By J. R. S. Fincham, W. G. Hill and E. C. R. Reeve

Genetical Research, Vol. 35, No. 2, 1980

On p. 181 the phrases ‘wild to mutant’ and ‘mutant to wild’ in lines 8–9 in the third paragraph should be interchanged: p and r are correction frequencies from mutant to wild and q and s are correction frequencies from wild to mutant, as is apparent in the Table immediately following.

On p. 188 the calculated ratios p/q and r/s may appear to be at variance with the values given in Table 2. This is due to the latter having been rounded to two significant figures. The more accurate values for the + × h3 cross are as follows: p = 0·043, q = 0·161, r = 0·157, s = 0·426 (firstsolution) and p′ = 0·026, q′ = 0·493, r′ = 0·243 and s′ = 0·128 (second solution).

On p. 191 (foot of page) some primes are misplaced. The correct formulae for r, q and s (as given on p. 182) are:

On p. 194, line 7, G = 2B + C should read G = 2B + D.