The importance of atherosclerosis in public health has generated a vast literature relating to epidemiology of the disease, clinical descriptions of symptoms and records of variation of serum concentration of cholesterol, triglyceride or lipo-protein fractions in normal or affected persons. Such evidence has led to a number of hypotheses as to the origins of the disease, and although rival theories may be espoused with fervour or may fluctuate in popularity, a familial predisposition to coronary disease is a recurring theme. In this brief review, which does not aim to be exhaustive and is not concerned with hypertension, we shall focus attention on the more important aspects and attempt to set the conflicting evidence in perspective.

Breeding tests of wild house mice, trapped from an isolated population from Sanday in the Orkney Islands, have demonstrated the presence of a semilethal t-haplotype designated tw106. Microscopic examination of sperm and testes from a sterile male obtained from this population revealed the histological characteristics typical for homozygotes for semilethal t-haplotypes. This report is the first description of the recovery of a t-haplotype from an island population of wild mice.

Plasmodial formation in the myxomycete Physarum polycephalum is controlled by a mating type (mt) locus, with heterothallic amoebae normally being unable to form plasmodia in pure clones. We report the isolation by mutagenesis of selfing mutants from heterothallic strains, and their analysis. Various amoebal strains of different mating types were mutagenized with a range of mutagens, and a number of selfing mutants (designated Het−) were isolated. A specific sensitivity of mt2 amoebae to mutagenesis by NMG was observed. This sensitivity segregated as a single locus closely linked or allelic to the mt2 locus. When the Het− clones were incubated at 30 °C, selfing was greatly inhibited. This property was used to determine the mt specificities of four Het− clones. The process of plasmodial induction in pure clones of CL was also studied using the 30 °C temperature effect.

The activity and thermostability of alcohol dehydrogenase (ADH) from 247 strains of Drosophila melanogaster were studied by spectrophotometric assay. The strains, in which second chromosomes had been made homozygous in a standard genetic background, were derived from five natural populations from diverse geographical and ecological sites. Evidence is presented that the majority of variation in ADH activity is attributable to the presence, in all five populations, of two electromorphs of the enzyme. However, some variation does exist between strains carrying the same electromorph, to some extent associated with variation hi body weight. Two strains showed atypical ADH activities. Variation in ADH thermostability was almost wholly attributable to the presence of two electromorphs; only two strains had enzymes with thermostabilities atypical of their electromorph. In the four strains with abnormal ADH properties the locus (loci) responsible map in the region of the Adh locus. Therelatively low level of heterogeneity within electrophoretic classes at this locus is discussed in view of recent findings at other enzyme loci in Drosophila.

Pyruvate kinase activity was studied in kidney extracts of mice from various sources. One C57BL/6J female among several hundred examined expressed activity approximately one half of the normal level. This animal transmitted the trait, and a single gene responsible for the activity difference was identified and mapped to chromosome 9. Linkage with Mod-1 and dilute was established. A spontaneous mutation in the C57BL/6J strain apparently was responsible for the variant pyruvate kinase.

Two hundred and two house mice (Mus musculus L.) from 29 populations in Europe and North Africa were typed for 16 H-2K and 17 H-2D antigens, each antigen defining a different allele. Among the 13 best characterized populations, 1 to 4 common and 3 to 20 rare antigens were observed. However, an average of 37% of the H-2K and 39% of the H-2D antigens remain to be identified. Ninety-four percent of the 50 mice tested were heterozygous for H-2K antigens and 89% for H-2D antigens. In 4 of the 8 populations tested, the most common H-2K and H-2D antigens occurred in the same individual more often than if randomly associated. Associations between common H-2K and H-2D antigens and excess heterozygosities may be the consequence of the small size and instability of populations composed primarily of related individuals. Estimates of the genetic distances between populations revealed that Danish, Egyptian, and several of the Orkney Island populations were related. These were the only populations in which metacentric chromosomes were not found. In contrast, populations which were antigenically different were also karyotypically different, regardless of taxonomic status of allozymic similarity.

Robertson, 1978, addressed the interesting problem of ascertaining the distribution of the time to detection of a recessive homozygote in a finite population. He was motivated in part by breeding and artificial selection practices. The same problem arises in the context of evolutionary processes and medical genetics since it refers to the time of first appearance as a homozygote of a new crossover event or a mutant gene.

The consequences of repeated backcrossing to a fixed parent are examined for haploid eukaryotes having a transitory diploid phase. The isogenicity attained in the absence of selected markers depends on the number of chromosomes and the total genetic map length, while the isogenicity of a chromosome carrying a selected marker increases more slowly and depends on the size of the chromosome. As inbreeding proceeds, the remaining non-isogenic material is not distributed evenly to all of the progeny. Instead, the majority of the progeny are completely isogenic with the fixed parent (with the exception of a region surrounding each selected marker), while the non-isogenic material is concentrated in a minority of the progeny. Even when the average isogenicity of the progeny and the fixed parent exceeds 99%, a significant proportion of the progeny will contain tracts of non-isogenic material which average several map units in length. Minor modifications enable these results to be applied to diploide. Examples show how to determine the degree of isogenicity produced by a given number of backcrosses in several specific situations.

In order to understand the evolution of genetic systems in which two genes are tandemly repeated (small multigene family) such as has been recently found in the haemoglobin α loci of primates, haemoglobin β loci of mouse and rarbit and other proteins, a population genetics approach was used. Special reference was made to the probarility of gene identity (identity coefficient), when unequal crossing-over is continuously occurring as well as random genetic drift, inter-chromosomal recombination and mutation. Two models were studied, cycle and selection models. The former assumes that unequal crossing-over occurs in cycles of duplication and deletion, and that the equilibrium identity coefficients were obtained. The latter is based on more realistic biological phenomena, and in this model it is assumed that natural selection is responsible for eliminating chromosomes with extra or deficient gene dose. Unequal crossing-over, inter-chromosomal recombination and natural selection lead to a duplication-deletion balance, which can then be treated as though it were a cycle model. The basic parameter is the rate of duplication-deletion which is shown to be approximately equal to 2(u + 2β)X, where u is the unequal crossing-over rate, 2β is the inter-chromosomal recombination rate and X is the frequency of chromosomes with three genes or of that with one gene. Genetic variation of the globin gene family, of which gene organization is known in most detail, is discussed in the light of the present analyses.

Spatial and temporal differentiation in Gerris lacustris and G. odontogaster (Heteroptera, Gerridae) were studied in restricted areas, where one population of each species was subdivided into several subpopulations. The aim of the study was to relate genetic population parameters to ecological population structure studied by mark-recapture methods in the same pond systems. Marked differentiation between the subpopulations and significant enzyme allele frequency changes between subsequent generations were found at several loci. It is suggested that non-selective forces are a sufficient explanation for the observed differences.

Retarded development of females (Symbol: Rf) has arisen spontaneously as a new trait in a chromosome mutant strain, which has an autosome fused to the original W chromosome. Female imagines with this trait emerge 1–3 weeks later than the males, due to retarded larval development. The proportion of female imagines is low. Rf is maternally inherited, it is neither expressed in nor transmitted through males. The evidence suggests that it is a dominant or epistatic factor on the autosomal part of the W chromosome-autosome fusion.

The non-random X chromosome expression that has been observed with coat markers in female mice heterozygous for the Xce alleles, Xcea and Xceb, has now been investigated with the electrophoretic enzyme marker, Pgk-1. Because the Xce status of the Pgk-1a marked chromosome was not known, PGK expression was assessed in Pgk-1a/Pgk-lb heterozygotes which carried either Xcea or Xceb on their Pgk-1b chromosome. The PGK-1A allozyme was found to predominate in both genotypes but when Xceb was present on the Pgk-lb chromosome the expression of the two allo-zymes was less unequal. This effect was seen in both liver and kidney of adults and to at least the same degree in embryos aged 13·5 and 7·5 days. The results have been interpreted to mean that the non-random X expression derives from a primary non-randomness of the X inactivation process and that a new and more extreme Xce allele, designated Xcec, was present on the Pgr-1a-marked X chromosome.

Cockerels singly or doubly heterozygous (t1/ +, t2/ + and tl/t2, respectively; collectively heterokaryotypic, HTK) for two different Z-autosome translocations (t1, t2) produce an array of chromosomally balanced and unbalanced spermatozoa owing to adjacent segregation and nondisjunction at the first meiotic division. This study addresses the developmental capacity of embryos derived from matings of control ( + / + ) and HTK (tl/ +, t2/ +, tl/t2) cockerels with hens bearing normal chromosome complements (+ /W).

Estimates of the hatchability of fertile eggs sired by + / +, tl/ +, t2/ + and tl/t2 cockerels were 82·8%, 43·0%, 41·3% and 10·9%, respectively. Approximately 75% of the mortality observed in embryos sired by HTK cockerels occurred by four days of incubation. Developmental arrest generally occurred earlier in embryos sired by t2/+ and tl/t2 cockerels than in those by tl/ + cockerels. These differences reflect variation in the degree of embryonic chromosome unbalance expected among embryos of the different sire groups. The pattern of mortality after three days was similar in embryos sired by HTK cockerels. In control embryos, mortality was highest on days 20–21 of incubation.

Chromosome analysis of 16/18 h embryos, day 1/5 embryos and hatched chicks sired by HTK cockerels revealed that most, if not all, chromosomally unbalanced embryos died during development; the majority before three days of incubation. Partial monosomy for chromosome one was found to be more deleterious to embryonic development than partial trisomy.

Linkage data and revised maps for 52 autosomal loci in L. cuprina are presented. Examination of the linkage relationships of biochemically and morphologically similar mutations in L. cuprina, Musca domestica L. and Drosophila melanogaster (Mg) suggests that the major linkage groups have survived largely intact during the evolution of the higher Diptera.

pMO1111, a derivative of FP110 carrying a Tn1 insert, has been used to generate two plasmid primes carrying Pseudomonas aeruginosa chromosome. pMO1112 has been shown to carry the pro-82+ gene and pMO1113 carries argH+ and lys-12+. pMO1112 is considerably more stable than pMO1113 in a recA+ background.

The selection component analysis developed by Christiansen & Frydenberg (1973, 1976) is a method to study the components of natural selection and is based on an analysis of population samples which include mothers and their progeny (mother–offspring combinations). Because only one progeny per mother–offspring combination is analysed, gametic selection and the reproductive components of selection in males are poorly characterized. We investigated the information which can be gained by analysing all progeny in each combination and showed that analysis of entire litters enables detection of gametic selection. Testing and estimation procedures are derived for this purpose. Sexual selection in males and mate preferences remain poorly characterized because the only information about the reproductive components in males is contained in the sample of male gametes and is insufficient to reconstruct the breeding structure of the male population. The format and interpretation of a selection component analysis is presented which takes these results into account.

The model of Lyon & Mason (1977) which defines three subregions of the t complex (T, tail-determining; A, abnormal transmission ratio; L, lethal) has been extended in an interpretation of male fertility data obtained from the combination of TOrl with different t haplotypes. The results demonstrate: (1) the T region of most t haplotypes (t12, t0, tw18 and tw2) possess gene(s) that interact with the L region to give quasisterility; (2) the T region of t6 lacks the allele(s) that result in quasisterility; and (3) the T region interacts with the A region to modify the transmission ratios of t haplotypes. The results were discussed in terms of an interacting genetic system controlling male fertility.

Mutants of [psi] a cytoplasmically inherited factor in the yeast Saccharomyces cerevisiae were isolated after treatment with a variety of agents including conventional mutagens and a number of compounds which cause loss of [psi] at high frequencies, namely methanol, KCl, dimethyl sulphoxide and guanidine hydrochloride. In [psi−] mutants the suppressor SUQ5 does not suppress ochre mutations such as ade.2.1.

Reversion analysis of the [psi−] mutants revealed three classes: (1) a class of agents producing [psi−] mutations which could readily revert to [psi+] (methanol, KCl and dimethyl sulphoxide belong to this class), (2) those which could not be shown to revert (GuHCl) and (3) the conventional mutagens which produced both revertible and apparently non-revertible [psi−] mutations. We conclude that GuHCl causes a deletion or loss of the [psi] factor. Methanol may cause an alteration of ‘state’ for example, of a promoter, and KCl may be selecting or inducing low copy number variants of [psi+] strains. It is possible that DMSO may be involved in regulation of [psi].

The electrophoretic variants of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1) have been used to investigate the randomness of X chromosome expression in the fetus and various extra-embryonic membranes of the mouse conceptus. The amnion shows essentially random expression of the maternally derived X chromosome (Xm) and the paternally derived X chromosome (Xp). The parietal endoderm, however, shows exclusive or preferential expression of Xm. The results support the idea that the randomness of X chromosome expression is correlated with embryonic cell lineage such that Xm is preferentially (perhaps exclusively) expressed in derivatives of the primitive endoderm and trophectoderm but that Xm and Xp are randomly expressed in the derivatives of the primitive ectoderm.

Experiments involving ovary transplants, embryo transfers or crosses with heterozygous mothers confirm previous findings that Xm is preferentially expressed regardless of the X chromosome expressed in the reproductive tract. Additional experiments show that the preferentially expressed X chromosome in the parietal endoderm and visceral yolk sac endoderm of a normal XmXp conceptus is always Xm regardless of grand-parental origin of Xm and regardless of whether the mother is a normal XX female or an XO female. Xp is, however, expressed in these tissues hi XpO female conceptuses. It is argued that a form of chromosome imprinting occurs at each generation to mark Xm and Xp as different and that this difference influences the choice of which X chromosomes are expressed in each cell lineage.

Internal sequences of Tn501(Hg) and Tn721(Tc) have been compared by hybridization. In spite of the difference in the resistance they code for, there is extensive homology between the two elements. This homology resides in the transposon-coded genes that are necessary for transposition and indicates that the elements are closely related.