ABSTRACTS OF PAPERS

ECOLOGICAL GENETICS OF PAPA VER DUBICJAl J . S. G ~ L E and M. J. LAWRENCE, Genetics Department, Birmingham University Xatural populations of Papaver dubiuin differ with regard to mean expression, variability and type of genetic control for several metrical characters. lnvcstigatioris i n progress aimed at extending and accounting for thew results u ill be discussed. POLYMORPHISM FOR CYAXOGENESIS IN LOTUS CORNICULATUS AND T R I F O L I U M REPENS DAVID A. JONES, Genetics Department, Birmingham University Both Lotus corn icuhtus and Trifolium repens are polymorphic for cyanogenesis. The problem is the interMctiori between thc polynorphisms i n mixed populations of the two species. Although it is easy to find wild populations of T. repens which do not contain L. corniculatw the reverse situation is relatively rare. It is possible, therefore, to study the effects of L. corniculatus on T. repens with some confidence, using the frwpency of cyanogenic plants in populations containing only T . repens as a refcrence control. It has bcrn found that in all the mixcd popillations samplrd so far the frequency of cyanogonic plants amongst L. corwiculatcis is invariably greater than that in T . repens. The basis for this cffect will be discussed. GENETIC CONTROL O F RECOMBINATION IN SCHIZOPH I'LLUM COMMUNE JUDITH A. STAMBERG and G . SIMCHEN, Biological Laboratories, Harvard University and Genetics Department, Birmingham University Mating compat ibility in t,he fungus Schizophyllwn commune is controlled by two unlinked factors, A and B, each of which is composed of two closely linked loci. Recombination between the loci of each factor has been st,udied and appears to be controlled by genes other than the factors themselves. Although A and B are similar in structure and function they are under separate recombination controls. The independence of these controls is shown by their different response to chnngcs in temperatnre and in genetic makeup. The extent to which thay affect. various parts of t3he linkage map will be examined and a comparison drawn between genetic control of rccomhination in Schizophyllum and other organisms. THE EVOLUTION OF DOMINANCE FOR METRICAL CHARACTERS M. .J. KEARSEY and B. BARNES, Genetics Department, Birmingham University Most previous considerations of the evolution of dominance have been concerned solely with major genes. However, there are good grounds for arguing that genes of gross effect, are of minor evolutionary significance md, as a consequenc~ of such gross effects, may exhibit special dominance relationships. This makes it difficult to discriminate between tfhe validity of the alternative theories of t'hu evolut,ion of dominance. The informat iori n o ~ available on the genetic architecture and selection of metrical characters allows a less ambiguous discrimination betwcrn these theories and the relevant evidence will be discussed in this light. HETJSROCHROMATIN XND THE REGULATION OF CHIASMA FREQUENCY B. JOHN mid G. M. HEWITT, Department of Genetics, Birmingham University and School of Biological Sciences, University of East Anglia Thr mode of rrgulat ion of chiasma frequency constitutes one of the most, fundamental, yet, intractable, prohlwns of geiictics. In natural populations of two species of short-horned grasshoppers a consistent corrrlntion txists betu-een the chiasma characteristics of individuals within a population and the occurrence of a chromosome polymorphism involving heterochromatic material. In one species (Myrmeleotettiz maculatus) The Genetical Xociety 325 the polymorphism involves supernumerary chromosomes, while in the other (Chor th ipp parallelus) i t takes the form of supernumerary segments on standard members of the complement. The study of the effects of heterochromatin in these two situations offers a direct approach to problems of chiasma regulation both a t cell and at population level. INVERTED CROSSING-OVER IN RELATION TO ANOMALOUS CHROMOSOME BEHAVIOUR AT RYE MEIOSIS 0. H. JONES, Department of Genetics, Birmingham University Investigations in a variety of plant and animal species have shown that bridges and fragments often occur at a high frequency in situations where inversion heterozygosity can be ruled out. Rather, these anomalies form part of a syndrome of errors which result from spontaneous breakage and reunion of chromatids at meiotic prophase. A recurring question is whether or not these abnormal events bear any relation to chiasma formation. The most compelling evidence in favour of this notion is the fact that the distribution of these events seems to be related to the distribution of chiasmata. This approach to the problem has been extended by camparing the distribution of these exchange events in contrasting rye genotypes which have widely different patterns of chiasma distribution. METHIONINE SYNTHESIS IN SALMONELLA T YPHIM URIUM: ITS REGULATION AND RELATION TO CYSTEINE SYNTHESIS D. A. LAWRENCE, M. A. QURESHI and D. A. SMITH, Department of Genetics, Birmingham University, and R. ROWBURY, Department of Botany, University College London The six structural genes concerned with methionine synthesis in S. typhimurium are not clustered together. Two pairs are closely linked (metd and H and metB and P) and the remaining two (metC and E ) are located separately on the bacterial genome. A seventh gene (metG) not associated with a specific enzyme is not linked to any of the others. Most mutants resistant to inhibition by one or more of the methionine analogues a-methyl methionine, ethionine and norleucine excrete methionine and have growth characteristics and enzyme repression patterns suggesting that they possess defects in the regulation of methionine synthesis. Their sites of mutation occur in three separate groups; the first closely linked to the metA and H genes, the second to metB and F and the third unlinked to any methionine gene. Mutation at sites close to those of the last group can result in suppression of the methionine requirement of a metG mutant. The construction of a comprehensive model for the regulation of methionine synthesis will be attempted. Recently mutants phenotypically distinct from known cysteine and methionine mutants with growth requirements for cysteine or methionine have been identified. They occur in a t least three closely linked and functionally distinct groups two of which are located within a cluster of five cysteine structural genes. The bearing of these results on the relationship between the synthesis of cysteine and methionine will be discussed. MATERNAL EFFECTS FOLLOWING STRESS IN A BEHAVIOURAL AND ENDOCRINE SYSTEM IN MICE AND RATS D. W. FULKER, Department of Psychology, Birmingham University Recent studies concerning the effects of prenatal stress on open field exploration in rats and mice and the cortico-steroid response to stress in mice indicate the importance of maternal inheritance in these behavioural and endocrine systems. The maternal effects observed appear to act in opposition to the additive genetic effects suggesting a buffering mechanism for moderating the expression of offspring genotype. The biometrical model used to detect this effect allows for the additive effects of maternal and offspring genotype but not for their interaction. An extension of the model is suggested which allows for the interaction. This maternaloffspring interaction model is compared with one which permits the detection of non-allelic interaction in maternal and offspring genotype. PSYCHOGENETICS : THE APPLICATION OF BIOMETRICAL GENETICS TO BEHAVIOUR P. L. BROADHURST, Department of Psychology, Birmingham University Phenotypes concerned with behaviour typically show continuous variation and can, like any other, be subject to appropriate analyses, especially those of biometrical genetics. Examples are drawn from a collaborative programme of research initiated in 1954 in which several aspects of behaviour in the laboratory rat have been studied. Emotionality as measured by defaecation and ambulation in a strange situation has been extensively analysed by diallel methods and also by bidirectional selection, now a t an advanced stage. 326 The Genetical Society Selection for phenotypes associated with escape-avoidance conditioning to shock in a shuttle box had also baon practised bidirectionally and descendants of the strains derived from the most famous psychogenetic experiment, that by Tyron for maze learning ability, have been studied. Findings from completed studies in this programme will be reviewed and some current work discussed. ON THE FUNDAMENTAL THEOREM OF NATURAL SELECTION A. W. F. EDWARDS, Department of Statistics, University of Aberdeen Fisher’s Fundamental Theorem of Natural Selection for a single locus under random mating will be discussed in detail. Special attention will be paid to the formulations by Fisher (1941, Ann. Hum. Genet. 11), Li (1956, Population Genet&; 1967, Nature, M . 214), Kempthorne (1957, An Introduction to Genetic Stat&&) and Kimura (1958, Heredity, 12). It will be shown that, except in the trivial case of no dominance in fitness, the theorem is an approximation in both discreteand continuous-time models. Its relation to the non-decreasing nature of the mean fitncss in the discrete model will be discussed. THE MEASUREMENT AND SIGNIFICANCE OF GENOTYPE x ENVIRONMENT INTERACTIONS IN PERENNIAL GRASSES E. L. BREESE, Welsh Plant Breeding Station, Aberystwyth Since the phenotype is the product of the genotype and its environment, it is just as apposite to grade an environment numerically according to the mean expression of a range of genotypes as it is to quantify a genotype by its average expression over a range of environment. Developing this concept, Finlay & Miilkinson (Ans. J . Agric. Res. 14, 742-54) found that the linear regression of the yield of individual cereal varioties on the mean of all varieties in a particular environment could be used to predict performance over a range of environments. E