An account is given of the habitat and ecology of a wrackbed population of Coelopa frigida (Fab.). The spatial distribution of the third-instar larvae was found to be patchy. This is due to a preference of adult flies for oviposition sites in zones of high temperature within the wrackbed. The relationship between larval density and temperature was found to account only in part for the patchy distribution, a second factor being the formation of family aggregates within each temperature zone. The effect of this type of spatial distribution on the interpretation of genetic sampling methods for the population is discussed.

Samples of third-instar larvae from the wrackbed population have been analysed for the presence of recessive embryonic lethals in three consecutive years from 1957 to 1959. From a total of 528 gametes tested, 44 recessive embryonic lethals were isolated. Cross tests for allelism showed that certain lethals were repeated within samples taken in the same year.

The gross frequency of embryonic lethals is shown to be independent of seasonal changes in population density. Estimates of gene frequency are made for certain individual lethals and these are shown to be greater than expected on the basis of the census size of the population. Possible causes of this discrepancy are examined.

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.

The recurring problem of negative interference in conjugal crosses of Escherichia coli K-12 (Rothfels, 1952; Cavalli-Sforza & Jinks, 1956; Wollman, Jacob & Hayes, 1956) has been periodically overshadowed by new discoveries concerning the mechanism of genetic transfer in this organism, such as unidirectional and partial transfer (Hayes, 1953; Wollman et al., 1956) and the genetic heterogeneity of zygotes formed in F+ × F− crosses (Jacob & Wollman, 1957), which have led to reappraisal of the interpretation of the genetic data. While some of those data (e.g. those of Rothfels, 1952) can be interpreted entirely on the basis of prezygotic elimination of the male genetic contribution, others (e.g. those of Cavalli-Sforza & Jinks, 1956) could not be, and were not, explained entirely on such a basis but demanded the introduction of the notion of incomplete pairing. Meanwhile the problem of negative interference became an important issue in other microorganisms such as bacteriophage, Aspergillus, Neurospora and yeast (review, Pritchard, 1960). The most plausible current model of localized negative interference in these organisms postulates that chromosome pairing is discontinuous and random, and that recombination only occurs within those small regions where pairing is effective (Pritchard, 1955; Chase & Doermann, 1958); thus the ‘coincidence of recombination in two intervals would occur with greater than random frequency if these intervals were short enough and close enough to be frequently included within one effectively paired segment’ (Pritchard, 1960). The mean distance over which such negative interference operates is very small, being of the order of only a few cistrons in both bacteriophage and Aspergillus (Pritchard, 1960).

Midget, a new dwarfing gene in the house mouse, was found in a line (NS) selected for small body size. Backcrosses to, and heterozygous matings of NS mice gave midget offspring in the expected 1:1 and 1:3 ratios. Backcrosses to two other lines of mice selected for small body size resulted in fewer midget offspring than expected and in a reduced phenotypic expression of the gene, though matings between these midget offspring gave all midget progeny.

A characteristic check in growth occurred between 15 and 21–24 days of age, and midgets rarely exceeded 10 g. at 6 weeks of age. They were 1·2 g. lighter than NS litter-mates at 3 weeks, and 3·6–4·4 g. lighter at 6 weeks. Fostering or transferring 3½-day-old midget embryos to the uteri of large mothers slightly increased the growth-rate, though the characteristic growth check still persisted. Transfer as embryos did not influence the midget phenotype.

Midget males were of near-normal fertility. The females were semi-sterile due to irregularity or absence of oestrous cycles, failure to ovulate, or the death of embryos before implantation. Each of these factors, which were also found in NS mice, could be remedied by the administration of exogenous hormones.

The genetic factors underlying the expression of midget are discussed, and the physiological traits associated with this and with other dwarfing genes are compared.

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 +.

Sixty-six independently produced markers have been tested for linkage with the A and B mating-type factors. Six loci linked with A and three linked with B were found. Maps of the two linkage groups which include the centromeres were constructed.

Non-identical alleles at two loci, paba-1 and chol-1, were found and crosses between different mutants were used to map the positions of the mutant sites within each locus.

1. A new hereditary defect affecting the hair coat of Swiss albino mice is described. The defect was found to be inherited as a recessive character and is designated as bare (ba).

2. The gene affected the vibrissae as well as pelage hairs. The lack of vibrissae and other sensory hairs at birth, helped to differentiate them easily from the normal animals. The first hairs on the body appeared at 13–14 days of age. The hairs were thin and tiny and remained there till about the thirtieth day. The hairs in the second hair cycle appeared at about 45 days, and again disappeared within 10 days. The animals were entirely naked when they were 6 months old.

3. Gross as well as microscopic examination of hairs in the first hair cycle did not show the four different normal types of hairs. The hairs were comparatively very small, thin, and the internal structure did not show any regularity in the arrangement of the air cells.

4. No difference was found in the number of hair follicles in the bare and the normal Swiss mice.

5. Histology revealed the presence of keratinized globular masses instead of straight hair. This abnormality persisted in all the hair cycles.

6. The bare mice were compared with the other mutants and placed in the Alopecia-Naked group where the abnormality was in the keratinization of the hair.

The usual conventions are relaxed to permit the introduction of a curved genetic model that shows some attractive features. Linear polygene analysis is examined in the light of this more flexible model. It is shown that great care is necessary in the choice of scale, since variances are more sensitive than means to small deviations from additivity. Inclusion of the F3 is necessary for successful prediction by extrapolation. The genetical validity of any type of polygene analysis is discussed. The new model is quite promising for the analysis of means; but I think that the (more ambitious) analysis of variances is likely to remain intractable, for both genetical and statistical reasons.

1. The growth of a number of inbred lines from the Pacific cage population have been compared under different conditions of temperature and nutrition. Body size and duration of the larval period were taken as measures of performance. Sub-optimal diets were provided by growing larvae on chemically defined synthetic media.

2. Gene-environment interaction is widespread and often very great. The phenotypic effects of inbreeding on body size, even on a live yeast medium, may be greatly influenced by temperature. In one set of comparisons, inbred lines averaged 20% smaller at 25° C. but only 3% smaller at 18° C.

3. Sub-optimal diets of different chemical composition, which lead to about the same average decline in body size, may differ greatly in the level of heterogeneity of response among the same set of inbred lines. Thus much greater heterogeneity was found on diets deficient in RNA than on diets with low protein levels. Such information is a useful guide to further study of gene-environment interaction in the outbred population.

4. Diets which lead to a decline in body size of flies of the foundation population do not necessarily cause greater proportional decline on the part of inbred lines. Individual lines have been encountered in which body size is quite unaffected by changes in diet which reduce the size of the outbred flies by 25% or more.

5. A series of crosses between lines from the same foundation population showed a striking level of homeostasis. The average body size and development time of the F1's was close to that of the population of flies on the favourable and two alternative sub-optimal diets. Also, compared with the parent lines, there was little evidence of gene-environment interaction among the crosses.

Dappled, a new completely sex-linked semi-dominant lethal mutation, is described. It is probably a new allele at the Mottled locus and has been given the symbol Modp.

Heterozygous adult females have a variegated coat very similar to that of Brindled and Mottled females; they have curly vibrissae at birth and some also have clubbed feet. All the characteristics are variable.

Hemizygous males die at about 17 days' gestation; they show a characteristic bending and thickening of the ribs and other skeletal defects. The cause of death is unknown.

The relative efficiency of three methods of selection (index, independent culling levels and tandem) is compared in terms of genetic gains in economic units. The comparison covers cases where variances, heritabilities and economic weights are unequal, while the case of two correlated characters is also examined. Various factors may influence the relative efficiency, including selection intensity, the number of traits under selection, the relative importance of those traits (in terms of a factor λ, which is the product of economic weight, heritability and phenotypic standard deviation), and the correlations between them.

The conclusions are:

(i) In all circumstances the index is never less efficient than independent culling levels, though in some cases it is no more efficient. Independent culling is, in turn, never less, but in some cases no more efficient than tandem selection.

(ii) The superiority of the index over other methods increases with an increasing number of traits under selection, but decreases with increasing differences in relative importance, its superiority being at a maximum when the traits are of equal importance. The superiority of the index over independent culling levels decreases with increasing selection intensity, but its superiority over tandem selection is independent of intensity.

(iii) The superiority of independent culling over tandem selection increases with increasing selection intensity or an increasing number of traits under selection, but decreases with increasing differences in relative importance.

(iv) The relative efficiency of the index over other methods is much affected by the phenotypic correlation between traits when the traits are of equal importance, the relative efficiency of the index being higher when the phenotypic correlation is low or negative. The effect of genetic correlation is only apparent when the traits are of unequal importance and its influence on relative efficiency changes with changes in other parameters.

(v) The relative efficiency of selection methods may be changed by their use for special purposes.

A systematic search for correlations between numerous minor skeletal variants in the mouse showed that these are few in number and feeble in extent. This apparent lack of integration is probably due to the fact that these characters are at the extreme limits of genetical determination and so are overwhelmingly influenced by chance in their manifestation.

The experiment was designed to form a bridge between the results of specific-locus experiments, using only a few gene loci, and those using the whole genome of the mouse. Male mice were given 600 r acute X-rays and bred from in such a way that at successive stages mutation in spermatogonia to dominant visibles and lethals, dominant semisteriles, recessive visibles and recessive lethals could be measured. The data concerning dominant mutations were relatively few but confirmed previous results. No recessive visible mutations were found, and the upper fiducial limit to the induced mutation rate to recessive visibles was set at a value 4500 times the rate to viable specific-locus mutations. From the attempt to measure recessive lethal mutations two interesting points emerged. The first was that granddaughters of the irradiated males had fewer corpora lutea per pregnancy than granddaughters of the control males, and the second was that this difference in number of ova shed was not reflected in any difference in litter-size at birth. Since this suggests intra-uterine compensation, no attempt was made to calculate mutation rates to recessive lethal genes from these data. The implications of the results are discussed.

In independent investigations, reported almost simultaneously (Cohen, 1960; Shreffler, 1960), the authors have described a protein variant system in the serum of mice, involving an electrophoretic difference in the iron-binding beta-globulin component, transferrin, and have shown the difference to be genetically determined by a pair of co-dominant alleles at a single locus. Both reports introduced the same gene symbol, Trf, for this locus, but in one, letter designations were used (Cohen, 1960), making the allele symbols TrfA and TrfB, and the three phenotypes TrfA, TrfAB and TrfB, while in the other, number designations were used (Shreffler, 1960), with the corresponding symbols Trf1, Trf2, Trf-1, Trf-1·2 and Trf-2. To avoid confusion in future reference to this locus, due to the two differing systems of nomenclature, the authors have agreed upon the revised nomenclature proposed in this communication.

A method for obtaining linear estimates of heritability and genetic correlation is given. It is based, essentially, on selecting, from a pedigreed population, prospective parents for which estimates of average genotype and phenotype values are obtained; a regression of genotype on phenotype value is then determined from a straight line fitted through points representing the population mean genotype and phenotype on one hand and the mean genotype and phenotype of selected parents on the other.

The method permits an evaluation of asymmetry in response for a trait selected in both directions, as well as asymmetry in correlated response to selection of two different traits, with data from a single pedigreed population.

Tipsy (symbol ti) is a fully penetrant recessive mutant in linkage group VII of the mouse. Homozygotes have a peculiar rabbit-like gait from the age of a week, followed soon after by a tendency for the fore-part of the body to sway from side to side, leading to a reeling locomotion with falling over in severely affected mice. There is marked variation in manifestation and some amelioration in older animals; both sexes are fertile.

Linkage relationships in group VII are discussed and tipsy is compared with other mutants showing locomotor instability.

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.

1. Antigenic polymorphism between individuals of the subspecies Peromyscus maniculatus gracilis is demonstrated.

2. Absorption analysis of heteroimmune rabbit sera using erythrocytes of individual mice revealed two unitary complete (saline) agglutinins, designated as anti-A and anti-B, reactive to erythrocytic antigens in this species.

Isoimmunization apparently demonstrated these same antigenic differences.

3. The two antigenic characters (A and B) defined by the agglutinins are inherited as if simply related to allelic factors designated PmA and PmB respectively.

4. These two antigens are found in representatives of both the subspecies P. m. gracilis and P. m. bairdii, and, in addition, the A antigen was observed in a laboratory stock of P. polionotus. Tested individuals of the species P. leucopus and Mus musculus, however, possessed neither antigen, and samples of human blood also lacked both antigens.

5. Species-specific agglutinins distinguishing individuals of the species P. leucopus and P. maniculatus, and population-specific agglutinins which distinguished between individuals of the subspecies P. m. bairdii and P. m. gracilis, have been observed.

A modest theory of polygene selection is presented. Recently published data show that the curved model of gene action (presented in a previous paper) is insufficiently general. The curved model does, however, show that the scaling tests (used in the additive type of polygene analysis) do not guarantee additivity; they guarantee a state of indeterminacy, in which additivity is one of a range of reasonable possibilities. These different possibilities give entirely different predictions of selective advance. The failure (in practice) of polygene analysis does not reduce the value of polygene concepts.