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.

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.

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.

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.

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.

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.

By nitrous acid or UV treatment ascospore colour mutants of two kinds, blue and colourless, were obtained in Aspergillus nidulans (wild-type has red ascospores). Four blue mutants were located in linkage group II within 0·5 unit of one another (locus symbol: b11). Of the colourless mutants, four were located in linkage group I within one unit of one another (locus symbol: c16), and one in linkage group IV (locus symbol: c14). In diploids the mutants were recessive. Colourless was epistatic to blue.

In crosses these characters behaved as ‘non-autonomous’ both in the ascospores and in the asci; all the ascospores of the asci in one perithecium as well as the perithecium wall were of the same colour. In crosses between strains with blue perithecia and strains with colourless perithecia, red, blue and colourless perithecia were found; each type included both crossed and selfed perithecia. Red selfed perithecia were of either parental genotype but blue or colourless selfed perithecia always had the corresponding genotype.

The phenotype of the perithecium (perithecial wall and ascospores) is considered to be determined by the homo- or heterokaryotic constitution of the protoperi-thecium which gave origin to it.

The frequencies of non-disjunction at first and second meiotic division, in both male and female of Drosophila melanogaster, are estimated. Numbers of exceptional individuals scored in several broods of increasing parental age are also presented. These results fail to show any evidence of an age-effect. Work claiming to demonstrate the existence of an age effect in Drosophila is reinvestigated. The importance of these results and their relevance to human studies are discussed.

Six years of data collected from two shifts of Cornell random bred control matings each year are analysed. Approximately 900 progeny were tested per year from 50 sires mated to 250 dams.

Means for the important economic traits are presented by years and regressions for nine such traits, together with their standard deviations, are shown. The only significant regressions are those for both egg production and specific gravity score in shift II. An abnormally low egg production the first year for this shift is considered responsible for this result and the reality of the regression is discounted.

Genetic variances are presented by trait and year. Year to year variability is evident, but no trends are indicated.

Estimates of heritability and genetic correlations between traits are presented. These estimates are considered to be quite reliable and will be useful as estimates of genetic parameters when this population is used in selection experiments. Estimates of heritability from the sire components of variance were as follows: 8-week body-weight, 0·29; 32-week body-weight, 0·48; 55-week body-weight, 0·44; age at maturity, 0·09; egg production to 500 days, 0·07; 32-week egg-weight, 0·51; 55-week egg-weight, 0·53; USDA albumen score, 0·29; blood spot score, 0·13; and specific gravity score, 0·34.

Important maternal effects were found for 8, 32 and 55-week body-weight, sexual maturity and egg production. Selection programmes should take into consideration the fact that maternal effects accounted for 13% of the total variation in egg production. Genetic correlations utilizing combined sire and dam components revealed no serious antagonisms between egg production and other economic traits. However, this conclusion must be considered in the light of what influence maternal effects may have, since correlations computed from sire and dam components separately may have opposite signs and be important.

The many negative estimates of interaction components (SH, genetic by environment) and (I, sire by dam) indicate that these elements of the model contributed little to the variation of the traits studied.

Acridine orange does not interfere with the distribution of the F-particles among the daughter cells but inhibits the multiplication of the episome.

In growing cells the generation time of the episome in the presence of acridine orange is longer than the generation time of the cell.

This lowers the number of episomes per cell to less than two copies at cell division.

F-particles rapidly multiply after transfer until a relatively small fixed number (3–4) is reached.