The numbers of members of three families of copia-like elements were counted on twenty X, 2nd and 3rd chromosomes collected from a natural population of Drosophila melanogaster. Theoretical predictions were computed for two models of copy number stabilization: (1) element frequencies are regulated by a simple genetic process such as copy number dependent transposition or excision, independent of chromosomal location; (2) elements are eliminated by natural selection against mutational effects of their insertion into the chromosome. Since insertions into the X can be expected to suffer more selection than autosomal insertions, due to expression of mutant phenotypes in the hemizygous state, hypothesis 2, called the disproportional model, predicts that the proportion of elements on the X will be smaller than the proportion of the genome contributed by the X, while hypothesis 1, called the equiproportional model, predicts that this proportionality will be unaffected. Two of the elements, 297 and roo, showed no evidence for deficiency of X-linked elements, but the data for a third element, 412, were consistent with the prediction based on the selective model.

These results indicate that simple selection against mutational effects of insertions of transposable elements is not generally adequate to account for their distribution within populations. We argue that a mechanism such as recombination between elements at different chromosomal sites, leading to rearrangements with highly deleterious, dominant effects could play a role in stabilizing copy number. This process would lead to a higher abundance of elements in genomic regions with restricted crossing over. We present some data indicating such an effect, and discuss possible interpretations.

Linkage studies with the mutant dreher (dr) of the mouse (Mus musculus L.) have shown that it lies in linkage group XIII and that the order of loci is dr–Dh–ln. The recombination between dr and Dh was 22·3 ± 4·1%.

Two previously undescribed pleiotropic effects of the dr gene were observed. The first was a tendency to white spotting in the belt region, and the second an interaction with brachyury (T) such that drdr T+ animals had shorter tails on the average than + dr T +.

A method is developed for calculating the probability of establishment of an allele which is favoured in some places, but not others, in a large subdivided population. This method is quite general, and could be used to calculate the chance that any system which is linear near an absorbing boundary will move away from that boundary. The results are applied to a population distributed along one dimension. Only mutants which arise within a distance ∼ σ/ √2s of the region in which they are favoured stand an appreciable chance of establishment. The net chance of establishment of mutations distributed randomly across the habitat will be decreased by gene flow if selection against them is sufficiently strong. However, if the mutations are only weakly deleterious outside some limited region, gene flow may increase the net chance of establishment.

Extracts of disomic wheat-barley addition lines were tested for the presence of a barley malt endopeptidase (MEP-1) by employing isoelectric focusing (IEF) and western blotting. The blots were probed with polyclonal antibodies raised against MEP-1 purified from the endosperms of 5-day-old germinated barley seedlings. The endopeptidase was detected in the Betzes barley cultivar and the addition line containing the full genome of the wheat cultivar Chinese Spring plus a chromosome 3 pair from Betzes barley. The endopeptidase was not expressed in Chinese Spring nor the addition lines containing other Betzes chromosome pairs. The endopeptidase was detected in a ditelosomic addition line containing the long arm of Betzes chromosome 3. We have concluded that the gene coding for MEP-1 (Cep-B) is located on the long arm of Betzes chromosome 3.

A new method is presented for estimating the rate of gene flow into island populations using the distribution of alleles in samples from a number of islands. The pseudo maximum likelihood estimator (PMLE) that we derive may be applied to species with either discrete or continuous generation times. For Wright's discrete-generation island model, the method provides an estimate of θ = 2Nm where N is the (haploid) population size on each island and m is the fraction of individuals replaced by immigrants in each generation. For a continuous-generation island model, the corresponding parameter φ is the ratio of the immigration rate φ to the individual birth rate λ. Monte Carlo simulations are used to compare the statistical properties of the PMLE with those of two alternative estimatorsof θ derived from Wright's F-statistics. The PMLE is shown to have greatest efficiency (least mean square error) in most cases for a wide range of sample sizes and parameter values. The PMLE is applied to estimate θ using mtDNA haplotypes and allozymes for subdivided populations of African elephants and Channel Island foxes.

Samples of the intertidal prosobranch Littorina saxatilis were collected along vertical transects from high- to mid-store levels at five different geographic locations of western Europe. Electrophoretic screening of ten metabolic enzymes revealed five highly polymorphic loci. Four of these showed no or few significant differences in allele frequencies between high- and mid-shore samples of Littorina saxatilis. The fifth locus, Aat (aspartate aminotransferase, EC 2.6.1.1), showed clinal variation in allele frequencies over the few metres of each transect, suggesting that this locus, or a coupled locus, is under selection with a slow allele (Aat100) favoured in mid-shore habitats and a faster allele (Aat120) selected for in the high littoral fringe.

1. In the course of evolution, complicated organisms have descended from much simpler ones. Since the instructions to form an organism are contained in the nucleus of its fertilized egg, this means that the genetic constitution has become correspondingly more complex in evolution. If we express this complexity in terms of its improbability, defining the amount of genetic information as the negative logarithm of its probability of occurrence by chance, we may say that genetic information is increased in the course of progressive evolution, guided by natural selection of random mutations.

2. It was demonstrated that the rate of accumulation of genetic information in adaptive evolution is directly proportional to the substitutional load, i.e. the decrease of Darwinian fitness brought about by substituting for one gene its allelic form which is more fitted to a new environment. The rate of accumulation of genetic information is given by

where Le is the substitutional load measured in ‘Malthusian parameters’.

3. Using Le = 0·199, a value obtained from the application of the ‘principle of minimum genetic load’ (cf. Kimura, 1960 b), we get

It was estimated that the total amount of genetic information accumulated since the beginning of the Cambrian epoch (500 million years) may be of the order of 108 bits, if evolution has proceeded at the standard rate.

Since the genetic information is transformed into phenotypic information in ontogeny, this figure (108 bits) must represent the amount of information which corresponds to the improved organization of higher animals as compared to their ancestors 500 million years back.

4. Problems involved in storage and transformation of genetic information thus acquired were discussed and it was pointed out that the redundancy of information in the form of repetition in linear sequence of nucleotide pairs within a gene may play an important role in the storage of genetic information.

If a polymorphic locus is maintained in finite populations by frequency-dependent selection with selective neutrality at equilibrium, it is generally accompanied by two genetic loads, i.e. the dysmetric and the drift loads. The former arises because the fitness of the population may not be at a maximum at the equilibrium gene frequency and the latter because genetic drift in small populations displaces the gene frequency from its equilibrium value.

In some simple models of frequency-dependent selection considered, the drift load is independent of selection coefficients and is approximately equal to (n−1)/(2Ne), where n is the number of alleles and Ne is the effective population size.

A new type of apparatus for replica plating is described, which reduces operator error and fatigue. Several replica plates can be made immediately, thus eliminating the need for a master plate in many cases.

1. Stock 540 of Paramecium aurelia (syngen or variety 1) contains two duplicate genes M1 and M2, each of which is capable of supporting growth of mu particles in the cytoplasm, thus producing the mate-killer phenotype.

2. Of six sensitive stocks of P. aurelia syngen 1, collected from widely separated localities, none contained either M1 or M2.

3. One sensitive stock (544), though proved to contain both recessive genes m1 and m2, gave aberrant ratios of mate-killers and sensitives following hybridization with stock 540. Evidence has been adduced consistent with the hypothesis that the m1- and m2-bearing chromosomes are involved in a translocation, by comparison with stock 540.

4. There is a proportionality between numbers of M genes and speed of killing, and presumably therefore with the number of mu particles.

5. Loss of mu particles following substitution of M genes by their recessive alleles occurs at times varying between eight and fifteen fissions after change of genotype.

This paper describes selective differences imposed by environmental ethanol on six genotypes at the alcohol dehydrogenase (Adh) locus in Drosophila melanogaster. Probit analyses were used to relate differences between the percentage survival of adults of different Adh genotypes to ethanol concentration. Regression analyses were used to relate differences between the pre-adult developmental times of different Adh genotypes to ethanol concentration. The directions of differences between some of the genotypes were found to differ in these two components of fitness. The differences in developmental time are linearly related to the differences in the in vitro alcohol dehydrogenase activity expressed by these genotypes. Percentage survival differences amongst adults are not linearly related to these differences in enzymic activity. The development of AdhF AdhF pre-adults is retarded the least on ethanol impregnated media but AdhFAdhS adults are most likely to survive on such media.

The results of a previous paper on the effect of optimizing selection, mutation and drift on a metric character determined by a large number of loci have been extended to include the possibility that, in addition to selection for an optimal value, there may be independent selection in favour of heterozygotes; it is assumed for simplicity that at each locus the heterozygote has the same advantage, s, over each of the homozygotes. Under selection alone there is a stable equilibrium if s > ca2, where c is a measure of the intensity of the optimizing selection and a is the effect of a gene substitution. Under the additional forces exerted by mutation and by drift due to finite population size each locus behaves independently of the other loci as if it had a heterozygous advantage equal to (s − ca2).