Twenty-four lines were bred from a base population of outbred Q mice by continued full-sib mating. Inbreeding depression in litter size at birth was observed. This decline in litter size was analysed in terms of ovulation rate, the incidence of preimplantation mortality and the incidence of postimplantation mortality. Pregnant females were dissected at 17½ days' gestation and the numbers of corpora lutea, or eggs, and of live and dead embryos were counted. Matings were arranged so that separate estimates of the effects of inbreeding in the mother and in the litter on the components of litter size could be obtained.

In the first generation of inbreeding when the inbreeding coefficient of the litter was raised from 0 to 25% decline in litter size was attributable to an increased incidence of preimplantation mortality.

In the second and fourth generations decline in litter size was attributable to (1) a reduction in the number of eggs ovulated by the inbred mothers, (2) an increased incidence of preimplantation mortality which resulted from inbreeding in the mother. No evidence of significant effects on mortality of inbreeding in the litter was obtained in the later generation of inbreeding.

These findings are discussed in the context of previous work on the effects of inbreeding and crossing on litter size and its components in mice and pigs.

1. Selection for long or short wings was carried out in three pairs of lines of which two were started from the same basic population. At the end of the selection experiment the frequencies of the chromosomal arrangements were determined in each line and compared with the corresponding original frequencies to see if the chromosomal polymorphism of Drosophila subobscura is related to the genetic variation of size in a regular way.

2. The three pairs of lines show an asymmetrical response to selection. Selection for long wings is less effective in changing the mean of the population than selection for short wings.

3. Heritability is lower in the lines selected for long wings, especially in the later generations of selection.

4. Viability shows a very small decrease during selection in most selected lines.

5. In no case does the coefficient of variability show statistically significant changes, but there is a general tendency for it to decrease.

6. Selection for long wings favours combinations heterozygous for the standard chromosome orders and specific complex inversion orders. Selection for short wings generally fixes in homozygous combination specific complex inversion orders.

7. The heterozygous combinations of the standard chromosomal orders, which are most frequent in northern populations, when combined with the complex inversion orders which are most frequent in southern populations, have a heterotic effect on size.

8. The complex inversion orders usually fixed in homozygous combinations in the lines selected for short wings are those most frequent in southern populations which have a smaller mean size than northern populations.

9. The blocks of genes integrated in ‘supergenes’ in the inverted segments of the chromosomes of D. subobscura differ in genetic composition with respect to the control of wing length.

Two codominant alleles, Mup-a1 and Mup-a2, controlling electrophoretic variation of one of the components of the major urinary protein (MUP) complex of the mouse Mus musculus have been found to be linked to the black–brown coat color alleles (linkage group VIII).

Following the transfer to the common pigeon (Columba livia) of a cellular antigen (Cg) from C. guinea, and to Streptopelia risoria of respective members of the group-8 system from chinensis and senegalensis, new combinations of these two antigenic systems were produced from matings of livia and risoria. The hybrid substances associated with the cells of each of the five new combinations of the cellular antigens were related to each other and to the usual F1-livia/risoria cells but, with the possible exception of two, were definitely differentiated from each other. Cross-reactivities of the reagents for the hybrid substances were also observed, primarily with heterozygotes of the group-8 system of Streptopelia. Evidence is thus provided that the interaction takes place primarily if not entirely between the genes of the C-system of Columba and the group-8 system of Streptopelia.

Three parameters of diuretic response to water-load (diuretic lag, maximum rate of diuresis and ratio of total output to input volume) have each responded to selection from a genetically heterogeneous base stock with significant realized heritabilities. Selection has been continued for ten generations and has produced mice more extreme than any of the founder strains. In the selection lines for ratio of output to input, correlated responses in salt excretion during the course of the diuresis, relative adrenal weight, the relative size of the renal medulla, and the quantity of renal collecting ducts, have been observed. These correlated responses are accounted for in terms of renal and adrenal physiology. The elucidation of the individual genetic determinants of the responses is discussed.

Results of crosses of a large number of Neurosporas of different origin, including several distinct strains of N. sitophila, were utilized to re-examine the question of whether certain wild-type Neurosporas other than N. crassa show biases in the two types of second-division segregation. Segregations for alleles of the mating type and peak loci on a wide variety of genetic backgrounds gave little evidence for excess either of symmetrical or asymmetrical ‘post-reduction’ asci.

Individual yeast strains show characteristic differences in the amount of chloramphenicol required to inhibit the synthesis of the respiratory system. This varies from 0·05 mg./ml. to 4 mg./ml. A correlation between chloramphenicol and tetracycline resistance appears likely but no correlation between chloramphenicol and erythromycin resistance was observed. These relationships were emphasized by cross-checking spontaneous resistant mutants for each antibiotic. Nearly all mutants showing spontaneous resistance to chloramphenicol had a simultaneous increase in tetracycline resistance but no increase in erythromycin resistance. Spontaneous resistance to erythromycin on the other hand, had no striking effect on tolerance levels to chloramphenicol and tetracycline. Increases in erythromycin resistance were commonly accompanied by an increase in resistance to other macrolide antibiotics. There are similarities between these effects and those described for certain bacterial systems.

We have isolated a number of λ dg HFT lysates which carry proximal fragments of the galactose operon. Most of these have been shown to be different, and each terminates in either the kinase or transferase cistron. They divide the kinase cistron genetically into seven blocks of mutants, and the transferase into eight.

When a λ dg is used to transduce a bacterium which carries a mutation in a cistron which is intact in the λ dg the transduction frequency is high in the presence of λ-helper. This is attributed to integration of the transducing fragment at the λ-attachment site and complementation between the two operons in the heterogenote. When the same λ dg transduces a mutation lying in the cistron in which the λ dg terminates, so that recombination within the galactose operon is obligatory, the transduction frequency is 10 to 1000 times less.

In such cases there is a general increase in transduction frequency between distal mutations (i.e. those lying near the termination of the deletion) and proximal mutations, but the relationship does not hold for many individual pairs of mutants, probably due to physiological differences between the bacterial strains.

1. Chromosome 6B of T. aestivum, to which a small segment of an Ae. umbellulata chromosome had been translocated, was examined both by interference microscopy and in stained preparations.

2. In the stained preparation a constriction was observed in the long arm of chromosome 6B and also a terminal knob that was also observed on chromosome A of Ae. umbellulata.

3. These features were also observed by interference microscopy and in addition the portion of the chromosome 6B of Transfer distal to the constriction had different phase-retarding properties.

4. It is concluded that the part of chromosome 6B distal to the constriction is the part of Ae. umbellulata chromosome A which carries the gene for the leaf-rust resistance of that species and of the wheat variety into which it was translocated.

Six experimental populations of D. pseudoobscura were maintained at three different temperatures for more than 8 years. All the populations have originally descended from the same founders. The populations were examined for evidences of genetic divergence. The pre-adult viabilities of the flies from these populations, and of their F1 and F2 hybrids, were studied at 16°C., 25°C., and 27°C. The results indicate that the populations have diverged genetically from each other. Some divergence is observed not only between populations kept at different temperatures, but also between the replicate populations kept at the same temperature.

A new neurological mouse mutant, Nijmegen waltzer (symbol nv), that causes circling and head-shaking without deafness, a marked tendency for aggressiveness, and reduced weight, is described. It is a single autosomal recessive, with complete penetrance and variable expression, and is probably located in linkage group I.

Non-directional asymmetry of paired organs is attributed to developmental ‘noise’. The level of asymmetry is inversely correlated to the degree of developmental stability. Children affected with familial cleft lip ± cleft palate have an increased asymmetry of their dermatoglyphics and molar teeth. The action of polygenes with a quasi-continuous distribution is consistent with this observation.

Recombination within the Y locus in Ascobolus immersus

By A. Kruszewska and W. Gajewski

Vol. 9, No. 2, p. 159 (1967)

In the legend to Fig. 1, p. 165, for ‘(in %)’ on lines 4 and 5 substitute ‘(× 103)’.

Recombination and incompatibility in Schizophyllum

By G. Simchen

Vol. 9, No. 2, p. 195 (1967)

On p. 207, line 9, for ‘½(nα + 1)’ read .

A new mutation, Em, is described for T. pyriformis, syngen 1. This dominant mutation eliminates the normal immature period in heterozygotes but is lethal in the homozygous state.

This paper is dedicated to Dr. Ralph Cleland in honor of his 75th birthday.

The sex factor of colE1a appears related to Ib, the sex factor of colIb, by each of three criteria: mutual inhibition of epidemic spread, antigenic structure of the sex pilus and susceptibility to I phage. The failure of each factor to spread in cultures carrying the other implies that donor ability is subject to a cytoplasmic repressor. Unlike two colI factors, colE1a and colIa (or Ib) can co-exist to give a doubly colicinogenic strain.