Sterility resulting from treatment of male rats with methyl ethane sulphonate and ethyl methane sulphonate was found to be due to the induction of dominant lethal mutations in spermatozoa and spermatids. Spermatids in the acrosome phase of development were found to be the most sensitive cells and at low doses of both compounds the majority of deaths occurred after implantation. The earlier cell stages, i.e. spermatogenia and spermatocytes, were the most sensitive to isopropyl methane sulphonate and Busulphan (Myleran). The action on spermatogonia was confirmed by spermatid counts and the time of occurrence of oligospermia or aspermia was calculated. Pre-implantation deaths occurred mainly in the early cleavage stages after both isopropyl methane sulphonate and Busulphan; at least part of these losses can be attributed to the induction of dominant lethal mutations in spermatocytes and early spermatids. Isopropyl methane sulphonate appears to be the more effective of the two drugs in this respect.

1. The development and morphology of the semi-dominant mutations Ragged and Opossum are compared. The results of the present study support evidence of previous linkage studies which suggest that Ragged (Ra) and Opossum (Raop) are alleles.

2. Examination of embryos from 18-day-old first parity matings of + + × Raop + reveals that there is no deficiency of Raop + embryos. However, in Ra + × Raop + and Raop + × Raop + matings some Raop + embryos die in utero in addition to the pre-natal death of the RaRaop and RaopRaop embryos.

3. In all matings of Ragged and Opossum, there is a high frequency of oedematous Raop + embryos. In + + × Raop + matings, the frequency of oedema increases with increased age of the embryos.

4. Although the pattern of hair follicle formation is the same in both the mutant and normal embryos, follicles begin initiation later in the mutant embryos. The delay in follicle initiation is increased in the following order: Ra +, Raop + (non-oedemic), RaRa and Raop + (oedemic).

5. Heterozygous Opossum and Ra + mice have a full complement of pelage follicle primordia, but some follicles fail to differentiate. The differentiating follicles pass through the same developmental stages and require the same time for development as follicles in + + mice.

6. Heterozygous Ragged and Raop + mice have a full complement of tylotrichs, whereas the concentration of awls is variable. In Ra + mice there is a reduction in zigzags, and Raop + mice usually lack zigzags. No auchenes are observed in the mutant mice.

7. Hair growth is asynchronous in Ra + and Raop + mice, with the exception of the first pelage coat. The quiescent phase of the hair growth cycle is short or even missing.

8. The degree of Ra and Raop gene activity is in the following order of increased severity: Ra +, Raop + (semi-lethal), RaRa (semi-lethal), RaRaop (lethal) and RaopRaop (lethal).

Body-weight and shank length from 2 weeks of age to adult (and from 8 weeks onwards, shank width) have been measured on 154 fowls all hatched on the same date, belonging to two F1 breed crosses: White Leghorn × Rhode Island Red (L × R) and Indian Game × Light Sussex (G × S). After logarithmic transformation the data have first been analysed cross-sectionally (analysis of the age-means for each sex and cross). A longitudinal analysis (fitting a regression line to the data of each individual) has then been made of the approximately linear portions of the curves. The following conclusions are drawn.

(1) Growth in shank length relative to body-weight between 2 and 10 weeks conforms closely to simple allometry. The coefficient of ontogenetic allometry (heter-auxesis), k, is approximately 0·4, being 0·02 higher in L × R than in G × S and 0·05 higher in males than in females. In females k declines (eventually to zero) after 10 weeks; the decline occurs about 4 weeks later in males. For shank width relative to body-weight k is about 0·25.

(2) At a given body-weight males have longer and thicker shanks than females; L × R have longer but thinner shanks than G × S.

(3) Within sexes and crosses there is highly significant individual variation in k, but the allometry lines do not pass, within the limits of error, through any single point. This implies that variation in relative shank length is complex in its ontogenetic origin.

(4) There is no appreciable correlation within sexes and crosses between shank width and shank length at a given body-weight; this implies (as does (2)) that variation is also complex anatomically.

(5) Differences in shape and rate-of-change of shape contribute only a small part of the total variation within sexes and crosses; most is due to differences in general size and general growth rate.

(6) Shank width at a given body-weight is positively correlated with body-weight at a given age (r = + 0·36 within sexes and crosses). This agrees with the finding that the coefficient of static allometry (allomorphosis) for shank width is much higher than the ontogenetic coefficient. For shank length the ontogenetic and static coefficients are approximately the same.

It has been suggested (Berry & Searle, 1963) that the discontinuous (‘quasi-continuous’) variants studied by Grüneberg et al. in the skeleton of rodents can be regarded as constituting epigenetic polymorphism in different populations. Comparisons have been made between the incidences of skeletal variants in house mouse populations collected from: corn ricks on a single farm in Hampshire; eleven separated localities in different parts of the British Isles; and nine other places throughout the world. These showed that the method could profitably be used for genetically characterizing and hence comparing populations. There was evidence suggestive of genetical drift between local populations and stabilizing selection over a larger area.

The intensity of negative interference in 28 crosses involving 14 allelic paba mutants in different combinations has been measured. Among selected cross-overs between two such mutants, when the distance between the mutants is large, additional exchanges on the distal side (relative to the centromere) greatly exceed those on the proximal side. With decreasing length of the interval of selection, the inequality disappears. It is suggested that this polarity may be the outcome of a undirectional process which imposes a time sequence on the recombination events within an effectively paired segment. Some alternative explanations of this result are discussed.

1. A recessive autosomal gene, dx, preventing the anaphylactoid reaction has been discovered in a stock of Wistar albino rats from the Agricultural Research Council, Compton.

2. Segregation occurred in the F2 generation derived from crossing pure-bred reactor rats and pure-bred non-reactor rats.

3. Non-reactivity was outbred into non-albino stocks and was shown to segregate independently of the albino gene c and not to be closely linked to the colour genes, P and A.

4. The mutation from Dx to dx may have arisen a few years ago in one of the Wistar colonies before it was split into sub-lines.

5. The dx gene is fixed in several brother-sister mated sub-lines and appears to be in equilibrium with Dx in some less inbred closed-populations.

1. A three-year study was conducted to test the efficacy of inter- and intra-specific blood transfusions in domestic poultry for inducing heritable changes in the recipients. The latter were pure-bred White Leghorns. Pure-bred Broad Breasted Bronze turkeys and New Hampshire chickens served as blood donors to two distinct lines of recipients. All injections started when the recipient chicks were 2–5 days old. Altogether, more than 3000 chicks from blood injected lines were involved in the study, conducted between 1959 and 1961 and distributed between the parental and three subsequent generations. Each injected chick received a total of some 155 ml. of whole blood in the course of a five-month injection period. An adequate number of control (non-injected) birds was used throughout. Observations were made on plumage colour, body-weight, egg-weight, egg-shell colour, fertility and hatchability. Furthermore, blood plasma and muscle tissue of appropriate birds were subjected to immunological, chromatographic and electrophoretic analyses.

2. On the basis of all these criteria, no evidence of heritable shifts in the direction of the donor organism was discerned among birds belonging to either of the two treated lines.

(1) A tail-skin grafting method was used to test for histocompatibility differences between members of thirteen sublines of C3H inbred mice, kept in a 1 r./night gamma radiation field for twelve generations, on the average, and separated from each other by about thirty-four generations.

(2) No homograft rejections occurred, so there was no evidence to suggest that mutations at histocompatibility loci had taken place in any of these sublines. Calculations show that this finding does not conflict with the idea that a fairly large number of loci are involved, having mutation rates similar to those already known in the mouse.

The effectiveness of the assortative mating of selected individuals in increasing selection response was tested, using abdominal chaeta score in Drosophila melanogaster. Three paired comparisons were made. In two sets of lines with 10 matings per line, individual score was used for selection and as the basis for the assortative mating. In the third set with 20 matings per line an index of individual and family score, designed to maximize rate of response, was used.

The intensity of selection was one in ten in all lines. Flies were raised in vials and individual pedigrees were kept.

In all comparisons, assortative mating gave a greater selection response, this being partly due to a greater realized heritability and partly to a greater selection differential. The effect of the assortative mating was largest in the index selected lines. With random mating, the effectiveness of the index selection itself when compared to individual selection was in accordance with theory.

In two comparisons, assortative mating increased the rate of inbreeding. The highest rate of inbreeding was observed with index selection and assortative mating, even though there were here twice as many matings as in the individually selected lines.

In the individual selection lines, the effective population size was 7·4 pairs of parents, compared to the actual value of 10 and in the index lines 7·0 compared to 20. In the former, only one-half of the matings in the initial generations made any permanent contributions to the line and in the index lines only one-third. Within generations and lines, there was a significant positive correlation between the mean score of a family and its inbreeding coefficient.

It is suggested that assortative mating is a method of increasing selection response in some situations. Its particular characteristic is that it becomes more powerful when the heritability is high whereas all of the other environmental aids to individual selection are more effective when the heritability is low.

Serum samples from 1963 Merino sheep were examined for serum transferrin type. Two of the five transferrin alleles previously described in British breeds of sheep, viz. T fA and T fc, were found, but T fB, T fD and T fE were absent. Evidence for seven further transferrin alleles was obtained. These alleles were coded T fF, T fG, T fH, T fJ, T fN, T fK and T fL in decreasing order of mobility of the zones they produce in starch gel.

Gene frequency data is presented for the populations studied.

In these experiments comparisons were made between the magnitude of the interaction of ‘pure’ strains and strain crosses of poultry with two types of environments—location effects and a restricted-feed versus a full-feed rearing programme. The ‘pure’ strains were closed flocks of White Leghorns that had been selected for increased egg production, while the strain crosses were the reciprocal crosses of all combinations of these pure strains. Data from four separate experiments in four consecutive years used for this study involved 8320 laying birds. Six traits of the adult laying birds were used for these analyses.

It was expected that the ‘pure’ strains would differ in performance amongst themselves to a greater extent than the strain crosses, and for the two traits, body-weight at housing and sexual maturity, this was found to be the case in three out of four years. These two traits were affected to the greatest extent by the rearing treatment. Also, the genotype-environment interaction variance was found to be significant and of important magnitude relative to the genetic variance for these two traits. Where the environmental effect was found to be smaller, the interaction variance made up a smaller proportion of the genetic variance.

A variable delay among mating pairs in the time between contact formation and the initiation of F transfer was found. The conjugation process has no effect on the multiplication of the recipient cell.

In liquid medium newly infecting F-particles multiply faster than the host cell.

The experiment strongly suggests that the number of episomes per cell is small and that the distribution of the F-factor among the daughter cells is non-random.

A study of the gene B6m, previously described as a modifier, revealed that it is a recessive resistance gene of moderate effect when homozygous. Its value in enhancing resistance to bacterial blight when in combination with other genes, in particular B2, is emphasized. The symbol for the gene is simplified to B6.

1. Mate-killer paramecia (derived from stock 540, P. aurelia) were treated with ribonuclease and 8-azaguanine to determine the effect of these two substances on the mu particles and metagons.

2. Ribonuclease destroyed the metagons in living paramecia but had no direct effect on the viability of the mu particles. The latter were however destroyed precisely after one fission of cells whose metagons had been eliminated by ribonuclease treatment.

3. Re-synthesis of metagons was found to take place between the second and third fissions after treatment with ribonuclease, if the dominant gene M2 was present.

4. Increasing the concentration of ribonuclease in the external medium, or in the duration of exposure of paramecia to ribonuclease, resulted in destruction of increasing proportions of metagons.

5. 8-azaguanine did not destroy metagons already present, but destroyed the mu particles immediately.

6. It is concluded that the results obtained with these two substances are consistent with the view that RNA is an essential constituent of metagons.

The structural changes induced by X-rays in cells at different stages of spermatogenesis were analysed in salivary gland chromosomes of Drosophila melanogaster and compared with the changes induced by formaldehyde added to the food (FF) of the larvae.

The different stages of spermatogenesis vary in sensitivity to X-rays when measured by the percentage of sex-linked lethals, by the percentage of spermatozoa carrying structural changes, and by the number of changes in 100 spermatozoa. The proportions of the different types of change (T, In, Rp, Df), however, are fairly similar in all stages of spermatogenesis, but entirely different from those found after FF treatment. This suggests that it is the mutagen and not the sensitive stage which is responsible for the characteristic pattern of the FF effects.

The differences between the effects of X-rays and of FF are attributed to the different proportions of potential breaks induced by these two mutagens. Evidence has been presented indicating that while most of FF induced breaks are potential (about 73%), most of the X-rays induced breaks are immediate. For the dose rate used in the present experiment (below 1000 r/min.) only a small proportion (4–10%) of breaks induced by X-rays was found to be potential.

The induction of dominant lethals after X-irradiation of dictyate, later meiotic stages, and the pronuclear stage after fertilization have been compared using the technique of induced ovulation in mice. The injection of gonadotrophins ensures that the time at which the synchronously dividing oöcytes reach any particular meiotic stage is accurately known. Embryonic lethality up to 13½ days was studied after 0 r., 100 r. and 200 r. acute X-irradiation. Metaphase I, anaphase I and metaphase II were the most sensitive stages, with LD50 's of about 120 r., 130 r. and 170 r. respectively. The dictyate and pronuclear stages were much less sensitive, with LD50's in the region of 500 r., and sensitivity rose steeply during prophase I. Numbers of corpora lutea decreased with irradiation, the decrease being greatest with irradiation at metaphase I and anaphase I. The ovulation of large numbers of eggs, which increased the preimplantation loss of embryos above normal, and the low luteal counts probably masked lethality to some extent. Results generally agree well with those reported in a number of plant and animal species.

1. A two-hour relative deficiency of nicotinamide, produced by maternal treatment with 6-aminonicotinamide, resulted in a maximum frequency of vertebral fusions following treatment on day 9·5 of gestation, and a maximum frequency of cleft palates following treatment on day 13·5.

2. Both defects appeared with higher frequencies in the A/Jax than in the C57BL/6J inbred strain.

3. The frequency of induced vertebral fusions in F1 embryos from crosses between the strains was higher when the father was from the A/Jax strain than when the mother was—a patroclinous reciprocal cross difference.

4. The frequency of induced cleft palate in F1 embryos from crosses between the strains was higher when the mother was from the A/Jax strain than when the father was—a matroclinous reciprocal cross difference.

5. Since the reciprocal cross differences in frequency of vertebral fusions and for cleft palates were in opposite directions, the hereditary factors influencing susceptibility to the teratogen appear to differ for the respective organ anlage. These differences appear to be, in part, cytoplasmic.

6. The frequency of induced cleft palate in the offspring of backcrosses of (untreated) F1 female hybrids to A/Jax males differed according to the cytoplasmic origin of the F1 mothers. Thus the susceptibility of an embryo to the teratogen appears to be influenced by factors transmitted through the cytoplasm.

Ten A factor mutants and an unlinked A suppressor mutant were isolated from fruit bodies formed by common A heterokaryons of Coprinus lagopus. All A factor mutants formed false clamps and lacked A mating-type specificity. Four A5 and two A6 mutants had functional α sub-units which were recovered in tests for intra-factor recombination in matings between mutant and wild-type factors. No functional β sub-units were recovered in tests of two of the A5 mutants and the two A6 mutants which possessed functional α sub-units. From three other mutants (two A5 and one A6) neither α nor β sub-units were recovered.

The suppressor mutant also formed false clamps but was recessive since stocks carrying it retained their A and B specificities when mated with wild-type testers. Fruit bodies formed by monokaryons carrying the suppressor mutant had pale gills bearing varying proportions of abnormal tetrads with less than four spores.

An additive-multiplicative model is found to describe diallel cross data rather well. Estimates of the model's parameters are highly correlated from generation to generation.

A probability distribution of chromosome separation to the poles was developed to test the randomness of movement of univalents in asynaptic material where a variable amount of meiotic pairing occurs. Two tables were calculated, one for 24 chromosomes which can be used for any even number equal or less than 24, and the other for 19 chromosomes which can be used for any odd number equal or less than 19.

Three Nicotiana hybrids, namely N. glutinosa × N. otophora, N. glutinosa, N. sylvestris, and N. tabacum × N. glutinosa, and one polyhaploid were investigated. All hybrids had a tendency towards an equal distribution of unpaired chromosomes to the poles. The polyhaploid N. tabacum (with a substituted N. plumbaginifolia chromosome) had an opposite tendency, i.e. towards a flatter distribution than expected from random distribution of univalents. A short discussion of the problem is given.