THE GENETICAL SOCIETY—ABSTRACTS of PAPERS of A1059metdphageswas Isolated on Minimal 5

Heredity 62 (1989) 281—288 The Genetica! Society of Great Britain

THEGENETICAL SOCIETY

(Abstracts of papers presented at the TWO HUNDRED AND NINTH MEETING of the Society held from 11th to 12th November 1988 at UNIVERSITY COLLEGE, LONDON)

1. Neutrality of two alleles of 2. Molecular studies of bovine Esterase-5 in Drosophila anti-testosterone immunoglobulins pseudoobscura: a perturbation- T. Jackson,* D. J. Groves,t B. Morrist and P. reperturbation test G. Sanders* * Molecular Biology Group, Department of Einar Arnason Microbiology, and t AFRC Antibody Development Institute of Biology, University of Iceland, Reykjavik, Group, Department of Biochemistry, University of Iceland. Surrey, Guildford GU2 5XH, U.K. Weare interested in improving the therapeutic Aperturbation-reperturbation testsselective properties of ovine and bovine immunoglobulins neutrality of 100/100/100/100/100 and to hormones involved in the reproductive cycle. 106/100/100/100/100,thetwo most common A mouse-bovine heterohybridoma has been alleles at the highly polymorphic X-linked locus produced which secretes a monoclonal antibody Esterase-5 in Drosophila pseudoobscura. A total of against testosterone. In order to investigate the 22 replicate populations are set up in cages, 11 binding of this anti-steroid immunoglobulin to tes- populations start at a frequency of 76% and 11 at tosterone we have cloned cDNAs for both the 21% of the 106 allele. Allele frequencies change heavy and light chain proteins. Studies to charac- directionally and decrease in both high and low tense these clones will be presented. populations as groups and reach equilibria of respectively 60% and 14% after 200-300 days. The directed changes of allele frequencies are due to 3.Cloning studies of a methionine natural selection. A hypothesis of balancing selection accounts for the pattern of allele frequency high-affinity transport system of changes and predicts a dynamic equilibrium. A Salmonella typhimurium neutral hypothesis equally well accounts for the N. A. Shaw and P. D. Ayling pattern leaving the Est-5 variants to drift at neutral equilibria. A reperturbation of allele frequencies Department of Applied Biology, University of Hull, in each population, creating 22 additional reper- Hull HU6 7RX, U.K. turbed populations with the original populations Thehigh-affinity methionine transport system of as controls, directly addresses the question of Salmonella typhimurium (encoded by the metD balancing selection or dissipated linkage effects. locus, formerly called metP) is believed to be of Allele frequencies do not change directionally the shock-sensitive category (Cottam and Ayling, among the reperturbed populations as a group. unpublished), and therefore should consist of one The hypothesis of balancing selection is rejected periplasmic and at least two inner membrane pro- in favor of the hypothesis of dissipated linkage teins (Ames, G. F. L., 1986, Ann. Rev. Biochem., effects. In conclusion the 100/100/100/100/100 55, 379). A library of a partial Sau 3A digest of S. and 106/100/100/100/100 are iso-fitness alleles of typhimurium DNA in the replacement vector, Est-5 A 1059, was obtained from Dr. R. Maurer. A series 282 THE GENETICAL SOCIETY—ABSTRACTS OF PAPERS of A1059metDphageswas isolated on minimal 5. Identification of a putative B- agar plus D-methionine by lysogenic corn- plementation of an E.coli metD mutant.One of chromosome specific sequence the clones was shown to have retained the activity from rye (Secale cereale) of a high-affinity methionine transport system. The metDinsertwas subcloned into the high M. J. Sandery, J. W. Forster and R. N. Jones copy number plasmid, pUC8, and four metD Genetic and Crop Biotechnology Group, Department isolates were selected in an E. coli metD strain. A of Agricultural Sciences, University College of clone carrying pUC8 with a 1.4 kilobase insert gave Wales, Aberystwyth, Dyfed SY23 3DD, U.K. a methionine uptake rate which was 30% that of DNAfrom a rye plant containing 611-chromosomes an E. coli metD strain, and showed slow growth was compared by restriction enzyme analysis with on D-methionine medium. Three other larger DNA from a plant lacking B-chromosomes. With metD plasmids gave wild-type or increased levels the restriction enzyme Dra 1, the 6B restriction of methionine transport. pattern shows the presence of a highly repeated Expression studies using in vitro and minicell DNA sequence, about 1200 bp in length, which is methods showed that the larger metD plasmids not visible in the OB restriction pattern. This encoded two additional proteins of molecular repeated sequence has been isolated and used as weight 40 and 34 kDal. Neither of these proteins a probe to investigate whether the sequence is appeared to be a periplasmic binding protein. B-chromosome specific, its relation to other rye repeated sequences and its position in the rye B 4.Conservation of a human chromosome. derived Y-specific sequence on the Y chromosome of the great apes 6.Detection of Ig and TcR gene M. Kalaitsidaki,* K. Kwok,t M. A. Ferguson- rearrangement in human Smith and J. M. Conner* lymphomas * Duncan Guthrie Institute of Medical Genetics, Glasgow G3 8SJ, U.K. v. Orphanos*, D. Anagnostou,t Th. tAFRCInstitute of Animal Physiology and Genetics Papadaki,t G. M. Maniatis* and A. Research, Cambridge, U.K. Atha n ass iado u * 1 Department of Pathology, Cambridge CB2 lOP, * Department of Biology, Medical School, University U.K. of Patras, Patras, Greece. GM6YIO,a human derived repetitive sequence, Laboratory of Hematopathology, General Hospital specific for the short arm of the Y chromosome, of Athens, "EVANGELIMOS'ç Athens, Greece. was shown by Southern blot analysis to hybridise Igand T cell receptor gene arrangements represent with DNA from male gorilla (Gorilla gorilla), male markers of lineage, clonality and differentiation of orangutan (Pongo pvgrnaeus) and male chimpan- B and T cells respectively. Detection of such zee (Pan troglodytes). To investigate its chromo- rearrangements in B and T cell neoplasms has somal localisation the sequence was utilised in in provided the basis for their molecular diagnosis situ hybridisation studies with metaphase chromo- and classification particularly in severe cases where somes obtained from chimpanzee, orangutan and immunological analysis seems to be unable to gorilla fibroblasts. GMGYIO was labelled by nick define lineage and clonality. We used probes which translation with biotin-1 1-dUTP and hybridisation detect rearrangements of the Ig heavy (JH)and was carried out according to the method of Garson k-light (CK)chaingenes or the TcR 13-chain (Co) er a!. (Nucleic Acids Res., 15, 4761—4770). and y-chain (Tv) genes and proceeded to genotypic Hybridisation signal was observed on the Y analysis of various cases of lymphoproliferative chromosome in all 3 cases. In the orangutan, there disorders. was signal only on the short arm of the Y, whereas Our results on CLL, Hodgkin's disease and in the gorilla the majority of the signal was non-Hodgkin's lymphomas agree with those re- observed on the long arm. In the chimpanzee it ported in the literature (O'Connor, N. I. J., 1987, was not possible to decide whether the signal .1. Pathology, 151, 185—190). occurred on the short or the long arm because the Reactive processes and lymphornas of double Y chromosome is particularly small. The possible phenotype is our main interest. Among the reactive significance of these findings is discussed. processes we detect cases of T cell lymphoma THE GENETICAL SOCIETY—ABSTRACTS OF PAPERS 283

(TcR gene rearranged-Ig genes in germline Mycobacterium paratuberculosis (paratb) is the configuration) as well as of B cell lymphomas (Ig causative agent of Johne's disease (regional genes rearranged-TcR gene in germline configu- enteritis) in ruminants. It is very closely related to ration or deleted). One of the former cases was Mycobacterium avium with which it shares 98% confirmed a year later as a T cell lymphoma by DNA homology (McFadden, J. J., 1988, J. Clin. immunocytochemical analysis. We are currently Microbiol., 25,796—801).However, M. avium using a TcR (y) probe in the analysis of reactive causes only sporadic disease in ruminants, whereas processes in order to obtain data concerning the paratb is a major pathogen causing chronic, fatal, differentiation of these processes. wasting disease. Conversely, unlike paratb, M Ig and TcR genes were rearranged while TcRy avium is a pathogen of birds. Paratb also differs gene was in germline in the three cases of lym- from M. aviuni in its requirement for an iron- phomas of double phenotype (B cell lymphomas) chelating growth factor (mycobactin) for growth studied so far. The evaluation of the usefulness of and in its extremely slow growth rate. We have TcR gene rearrangements in the genotypic analy- isolated and characterised a mycobacterial inser- sis of these lymphomas is also desired. Analysis tion sequence (MIS1) which is present in identical of further cases is in progress. multiple copies in the genomes of all strains of paratb, but absent from all strains of M. avium. We propose that infection of an M. avium strain 7.Selection in karyotypic hybrid with MIS! has recently occurred leading to the zones rapid evolution of the species M. para tuberculosis. We also propose that insertional mutagenesis may J. B. Searle account for the multiple phenotypic differences between paratb and M. aviurn. The newly evolved, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, U.K. debilitated paratb may be an example of what Goldschmidt (The Material Basis of Evolution, Heterozygotesfor chromosomal (structural) re- 1940) termed a "hopeful monster". arrangements produced when karyotypic races hybridize in nature are expected to suffer reduced fertility relative to "pure" race individuals, as a 9. result of chromosomal imbalance or loss among Analysis of dines and linkage germ cells, associated with meiotic aberrations. disequilibrium in Heliconius The width of the zone of hybridisation between butterflies the races is expected to vary according to the extent of this fertility reduction. Other selective forces James Mallet related to karyotype may operate in the hybrid Galton Laboratory, Department of Genetics and zone. For a certain heterozygous karyotype, selec- Biometry, University College, Wolfson House, tion should favour individuals less prone to meiotic 4 Stephenson Way, London NW1 2HE, U.K. aberrations. There should also be selection for Narrowzones of hybridisation between colour pat- karyotypes which cannot or are unlikely to produce tern races are common in unpalatable insect aberration-prone categories of heterozygote. species. Such zones can be maintained if predators Studies on the common shrew (Sorex araneus) attack locally unfamiliar warning colour morphs and house mouse (Mus musculus) indicate that more readily than locally common morphs: these processes do occur in karyotypic hybrid frequency dependent selectiorL would then favour zones in nature. the predominant form on each side of a hybrid zone. A hybrid zone between races of Heliconius erato 8.Rapid speciation of was sampled in Amazonian Peru. Three unlinked mycobacteria by infection with loci were found to determine the major differences DNA transposable elements of warning pattern between races. A mark-recap- ture experiment showed that selection was strong: J. J. McFadden, E. Hull and J. Hermon-Taylor the fitness of introduced insects with unusual Department of Microbiology, University of Surrey, colour patterns was about half that of controls with Guildford, Surrey GU2 5XH, U.K., and Department of the normal local colour pattern. Sample data, con- Surgery, St. George's Hospital Medical School, sisting of gene frequencies and genetic associ- London SW17 ORE, U.K. ations, were fitted to theoretical models in order 284 THE GENETICAL SOCIETY—ABSTRACTS OF PAPERS to estimate both selection and gene flow indirectly. offspring resemblance and the expression of In Peru, the estimated per locus selection pressures genetic and environmental variance estimated by averaged about 20%, and gene flow was about full-sib analyses are discussed. 2 km per generation. In this study, direct and indirect measures of selection both showed that selection on individual 12.A novel source of genetic genes can be strong. In addition, the work illus- trates how measurements of hybrid zones can lead variation in ryegrasses to robust inferences about natural selection and R. N. Jones, H. A. Francis and Lutful Hassan population structure in the wild. Genetics and Crop Biotechnology Group, Department of Agricultural Sciences. University College of Wales, Aberystwyth, Dyfed SY23 3DD, 10.Phenotypic plasticity for life U.K. history traits in Drosophila Coichininetreatment applied to seedlings of per- melanogaster ennial ryegrass (Lolium perenne) and Italian ryegrass (L. multtflorum) induces heritable changes Martin D. Gebhardt and Stephen C. Stearns in several characters of agronomic usefulness in Zoologisches Institut der Universität Base!, CH-4051 diploid inbred lines. The changes are stable over Base!, Rheinsprung 9, Switzerland. several years of vegetative growth in the treatment generation, and they are also transmitted through Developmentaltime and dry weight at eclosion the selfed-seed to the generation following were analysed genetically in environments treatment. different in yeast concentration using a 6 x 6 diallel design of crosses. Genetic variances and covari- ances were strongly influenced by the environment and were different for the two sexes. Strong genetic 13.Theoretical and actual causes maternal effects were expressed in the poorer of gene conversion disparity, for environments. Significant dominance components different types of mutation and a standard test for epistasis suggest that genetic variances were mostly due to allelic interactions. B. C. Lamb However, computer simulations using an explicit Department of Pure and Applied Biology, Imperial genetic model indicate that this test may be sensi- College of Science, Technology and Medicine, tive to small biases of the allelic frequencies due London SW7 2BB, U.K. to sampling error. Thepossible causes of disparity in the direction of meiotic gene conversion at a heterozygous site are considered, using a wild-type(+)/mutant(m) 11.The effect of food deficiency example. They include: (i), disparity in the direc- on the expression of genetic and tion of correction of mispairs or non-pairs in hybrid DNA (hDNA); (ii), disparity in the environmental variances of body frequencies of invasion by the two types of size in great tits chromatid (+ bearing and m bearing) in asymmetric hDNA formation; (iii), disparity in the Sabine Henrich and Arie van Noordwijk frequencies of invasion by the two strands of a Zoologisches Institut der Universität Base!, CH-4051 DNA double helix at the site (3'5' invasions not Base!, Rheinsprung 9, Switzerland. equal to 5'3' invasions); (iv), disparity in double- Heritabilitiesof final weight and tarsus length of strand gap frequencies in the two types of nestlings were measured in a single population chromatid (+ bearing and m bearing) at the site. during the last three years. Cross-fostering experi- The amount of disparity is also influenced by the ments were performed to separate genetic and relative frequencies of symmetric and asymmetric environmental factors. In contrast to earlier years, hDNA, and of double-strand gaps, by the correc- food became scarce during the second half of the tion frequencies at the two mispairs, and by inter- 1988 breeding season. This influenced final weight actions of these various factors. and survivorship of nestlings profoundly. The Some of these causes should give disparity for effects of severe food limitation and parent— all types of mutation, including large deletions; THE GENETICAL SOCIETY—ABSTRACTS OF PAPERS 285 others will only do so for certain types of mutation. 16. The evolution of ageing Data from fungi are examined to find which of these causes of disparity actually operate. There Linda Partridge is strong evidence for (i), (ii) and (iii) occurring Department of Zoology, University of Edinburgh, in Ascobolus immersus (Zwolinski and Lamb, 1987, West Mains Road, Edinburgh EH9 3JT, U.K. Heredity, 59, 155-156, and unpublished). Ageingis a deleterious character whose evolution needs to be explained. The talk will deal with the major theories of ageing and their empirical basis. 14.Phenotypic models of evolution 17.Theory, experiment and reality John Maynard Smith of molecular evolution School of Biology, University of Sussex, Falmer, Manfred Eigen Brighton BN1 gaG, U.K. Max-Planck-lnstitut für biophysikalische Chemie, Usually,phenotypic evolution is of necessity ana- Gottingen, F. R. G. lysed in the absence of specific genetic information, by optimisation theory, or, if fitnesses are Thelecture will deal with new concepts in frequency-dependent, by evolutionary game evolutionary biology such as "sequence space", theory. What are the advantages and disadvantages "quasi species" and "statistical geometry". After of these methods? What assumptions about a brief introduction of these theoretical concepts, genetics must hold if they are to be justified? What experiments will be described that allow for quan- kinds of problem cannot be treated in this way? titative tests. The experiments include cloning of mutant distribution of RNA molecules produced de novo by Qreplicaseand determining their sequences. Similar in vivo experiments using phage QandE. co/i as a host have been carried out. 15.The evolutionary genetics of Subjecting such systems to selection pressure quantitative characters causes them to adapt to new environmental conditions. Several types of automatized evolution William G. Hill machines are described. Applications to viral sys- Institute of Animal Genetics, University of tems will be discussed. Edinburgh, West Mains Road, Edinburgh EH9 3JN, U.K. Muchof our knowledge of the potential rates and 18.Could natural selection be extent of evolution of quantitative characters responsible for molecular evolution comes from laboratory experiments. These show that directional selection can change traits to well and polymorphism? outside the original distribution, and can do so in John H. Gillespie a few generations. Analyses show that substantial inputs of variation arise from mutation, and theo- Department of Genetics, University of California, retical studies suggest and experiments illustrate Davis, California, U.S.A. that this can enable continued responses. So there Ashort review of recent work showing that various is obvious scope for adaptation. Indeed it is harder patterns in the molecular evolution and poly- to explain how populations maintain both a nearly morphism data are not compatible with current constant mean phenotype and much genetic vari- versions of the neutral allele theory will be pre- ability. sented. This will be followed by a description of A fundamental problem in the analysis of short a class of models of molecular evolution and poly- or long term changes in natural populations is to morphism due to the action of natural selection determine what, if any, selective pressures were that is in remarkable agreement with much of the acting to produce these responses. Conclusions molecular data. These models have a mathematical drawn often depend on which traits are actually structure that is similar to that of the strictly neutral recorded and are based on one or very few popula- model, although they differ in the predictions tions, so drift and selection cannot be disentangled. about the distribution of nucleotide substitutions. 286 THE GENETICAL SOCIETY—ABSTRACTS OF PAPERS As an example, a model of natural selection in a 21. Comparative molecular fluctuating environment will be described. This model will be analysed using the method of strong embryology as an approach to selection, weak mutation limits. study the relationship between development and evolution Michael Akam,* Alfonso Martinez-Arias,t 19.The evolutionary biology of lain Dawson,* Guy Tear* and Robert Kelsh* transposable elements * Department of Genetics and t Department of Zoology, Downing Street, Cambridge CB2 3EH, U.K. Brian Charlesworth Thehomeotic and segmentation genes of Department of Biology, University of Chicago, Drosophila form a regulatory hierarchy that directs Chicago, Illinois 60637, U.S.A. pattern formation in the early embryo. Many of Thedynamics of transposable elements in natural these genes have been highly conserved in evo- populations will be considered from a theoretical lution, so it is possible to identify their structural standpoint; and the predictions of the various homologues in distantly related species. We have models compared with data from natural popula- embarked on a project to identify these tions of Drosophila. Evidence will be presented homologues in the locust Schistocerca gregaria. Our that most of this information agrees with the view object is to relate differences in the morphology that transposable elements are parasitic DNA. and development history of these two insects to changes in the regulation and function of specific genes. 20.Metabolic constraints in evolution 22.The interconversion of purine Richard Beeby and Henrik Kacser ribonucleotides in wild-type and Department of Genetics, University of Edinburgh, APRT-deficient Friend Edinburgh EH9 3JN, U.K. erythroleukaemia cells Wewish to discuss how the metabolic and enzy- Franklin M. Amara and P. Gerald McKenna matic composition of the modern cell evolved from its primitive ancestor. Assuming that such an Biomedical Sciences Research Centre, University of ancestor contained few and low-activity proto- Ulster, Coleraine BS52 iSA, Northern Ireland. enzymes with very broad specificities, whose InFriend mouse erythroleukaemia cells, deficiency nature was determined by some kind of genetic of the purine salvage pathway enzyme, adenine material, one allows these "genes" to mutate and phosphoribosyl transferase (APRT) results in duplicate and delete randomly. The effects of these increased sensitivity to mutagenesis (Wilkinson, changes are reflected in the different rates of meta- Y. A. eta!, 1988, Genome, 30,suppl.1; Ward, P. E. bolic output, of which the enzymes themselves are and McKenna, P. G., 1987, Mutation Res., 180, the most important. Clones with different growth 273—276). Wild-type Friend cells (clone 707) were rates arise and this constitutes the natural selection compared with APRT-deficient mutant subclones in this early phase. The outcome is a diversification (707 DAP8 and 707 DAP1O) with respect to the of types of enzyme tending towards mono- metabolism of labelled exogenous hypoxanthine. specificity, Early stochastic events determine and The APRT-deficient subclones were found to have restrict the paths such evolution can take, while higher levels of two enzymes of the de novo purine the inherent metabolic constraints set limits to the pathway, adenylosuccinate synthetase (356%, phenotypic possibilities. Starting from the same 481%) and guanosi ne 5 '-monophosphate reduc- initial composition of the ancestral cell one can tase (178%, 161%) relative to clone 707. The rela- "repeat" the evolution but ends up with different tive enzyme activities paralleled the enhanced "solutions" (in number and types of enzymes) capacity for the incorporation of hypoxanthine to while the final growth rates are not greatly different. adenine rather than to guanine nucleotides in the The modern cell is one of these, relatively arbitrary, ratios of 10 and 11.92 for the APRT-deficient sub- solutions which thereby determines the nature of clones relative to wild-type cells. There was also the genes which sustain it. a significantly increased turnover rate of inosine THE GENETICAL SOCIETY—ABSTRACTS OF PAPERS 287 5'-monophosphate in the APRT-deficient sub- 24. Analysis of aprtmutantsof clones relative to wild-type cells. It is proposed on the basis of these results that the Friend erythroleukaemia cell in Friend cells, the lack of the salvage pathway line enzyme APRT may be partially compensated for O'Neilland Ivor Hickey by the divergent capacity of the hypoxanthine Rosemary metabolism in the purine de novo pathway to selec- Department of Biology, The Queen's University of tively yield adenine nucleotides for ATD-depen- Belfast, Belfast BT7 iNN, Northern Ireland. dent processes. Clone707 of the Friend erythroleukaemia cell line (FEL) has been shown to exhibit high mutation rates for two genes, thymidine kinase and adenine phosphoribosyl transferase, while being stable for other markers including resistance to thioguanine, 23.The role of ouabain and cytochalasin B. Loss of thymidine kinase, as in a number of other rodent cell lines, deoxyribonucleotide triphosphate is associated with DNA methylation. We have pools in the maintenance of error- examined a large number of independently iso- free DNA repair processes in lated aprt mutants to determine whether they can Friend mouse erythroleukaemia be restored to wild-type by treatment with the hypomethylating agent 5-azacytidine. In all cases cells it was found that although treated cells could form Yvonne A. Wilkinson and P. Gerald McKenna clones in the selective medium AAT they were unable to utilise exogenous adenine. Biomedical Sciences Research Centre, University of The aprt gene is located on mouse chromosome Ulster, Coleraine BT52 iSA, Northern Ireland 8. This is easily identified in FEL cells as a centric Friendmouse erythroleukaemia cells deficient in fusion with chromosome 6. Each cell contains two the salvage pathway enzyme, thymidine kinase, copies of this fusion product. The two 6/8 chromo- exhibit increased sensitivity to cell killing and somes may be distinguished as only one can be mutagenesis by: the physical mutagens, ultraviolet silver stained. We have cytogenetically examined irradiation (McKenna, P. G. and Hickey, I., 1981, spontaneous and mutagen induced aprt mutants Cell Biology International Reports, 5, 555-561) and to determine if loss or balanced reduplication of gamma irradiation (McKenna, P. G., McKelvey, one copy of this chromosome was responsible for V. J. and Frew, T. L., 1988, MutationResearch, the high rate of mutation. All mutant clones 200,231-242)and by the chemical mutagens: retained both copies of this chromosome indicating ethyl methanesulphonate, methyl methane- that chromosomal changes are not involved in the suiphonate, N-methyl-N'-nitro- N-nitro- production of aprt mutants. soguanidine and mitomycin C (McKenna, P. G. and Yasseen, A. A., 1982, Genetical Research, 40, 207-212). Deoxyribonucleotide triphosphate 25. pool measurements in cycling Friend eryth- An epigenetic theory of rapid roleukaemia cells show differences between wild- evolution type clone 707 cells and thymidine kinase-deficient clone 707 BUF cells (dATP-130%, dTTP-39%, D. J. Pritchard dGTP-50%, dCTP-99%, representing dNTP levels Department of Human Genetics, University of in clone 707 BUF cells as a percentage of the levels Newcastle upon Tyne, Newcastle upon Tyne in wild-type clone 707 cells). Thus pooi differences NE2 4AA, U.K. which already exist in cycling clone 707 BUF cells, Conventionalevolutionary theory fails to account together with any dNTP pooi changes induced by adequately for the speed of adaptive evolution, or mutagen treatment may render DNA repair pro- for apparent differences in evolutionary stability cesses error-prone and thus account for the of phenotypic strains. A new theory is proposed increased mutagen sensitivity observed in that provides an explanation of these features, thymidinekinase-deficientFrienderythro- as well as convergent evolution, canalised develop- leukaemia cells. ment, heterochrony and the coexistence of regula- This research was supported by the Leukaemia tive and mosaic developmental controls. A com- Research Fund. mon evolutionary theme is recognised in the 288 THE GENETICAL SOCIETY—ABSTRACTS OF PAPERS progressive attainment of genomic independence progressive genetic underpinning of phenotypic of the external world. adaptation to specialised conditions. All organisms acclimatise to their surround- With continued selection, late acting stimuli ings, but individuals vary in this capacity. It would are considered to be replaced by others acting be expected that alleles which favour acclimatisa- earlier in ontogeny, so that development of adap- tion and which are already dispersed throughout tive traits becomes initiated at progressively earlier a population would accumulate in survivors of stages (heterochrony), or is reinforced by addi- continued environmental selection. Experiment tional stimuli (canalisation). Eventually the most has shown that under such conditions already- ancient and fundamental traits could become adapted individuals can eventually arise. Evolu- defined by morphogens laid down in the egg or tion of preadapted states involves recognition of early embryo, in accordance with mosaic, as dis- internal stimuli which replace those that originally tinct from regulative control. Such a sequence impinged on the organism from outside. This inter- should allow phenotypic specialisation to proceed nalisation of control is seen as the first step in the relatively rapidly towards perfect adaptation.