A population genetic model is developed and then applied to the synonymous gene sequence variation observed in samples of the Human Immunodeficiency Virus Type 1 (HIV-1). The samples, which were taken from several previous studies, contain sequences of the envelope glycoprotein gene (gp 120) of HIV-1. This analysis suggests that the viral population within an infected patient at any specific time is likely to be composed of close relatives. The viruses in a sample are likely to share a recent common ancestor probably due to consistent positive selection for non-synonymous mutations coupled with low recombination in this region of the genome. There is no substantial difference in synonymous evolutionary rate between samples of sequences obtained from Peripheral Blood Mononucleate Cells (PBMCs) and samples taken from blood plasma. This is likely to be due to the high rate of migration between these 2 HIV sub-populations. The mutation rate for the genetic region examined is estimated at 9·20 × 10−4 per site per month. Under the assumptions of the estimation procedure, this estimate can be bounded between 8·50 and 9·91 × 10−4 with 95% confidence. When coupled with direct estimates of mutation rate, the rate of synonymous evolution suggests that the mean number of generations per month for HIV-1 in vivo is between 1 and 4.

We consider genetic models for the inheritance of the particular colour patterns of silver foxes. The models are evaluated by computation of statistical likelihoods based on observations of related foxes in extended pedigrees. Problems caused by incomplete paternity information are addressed by inferences based on phenotypic observations. The unreliability of subjective evaluations of fur colour also provides difficulty, in particular crossfoxes emerge as being difficult to differentiate. No evidence of linkage between Agouti locus and Extension locus is found in this dataset.

In order to understand the evolution of female mate preferences it is important to determine whether the genes for the preference and those for the preferred character are linked. It has previously been shown that female preference in the seaweed fly, Coelopa frigida, varies with the αβ inversion system on chromosome I. This inversion system is known to genetically determine, at least in part, the male preferred character, large size. This study was undertaken to determine whether the genes determining mate preferences, as well as those determining female receptivity, co-inherit with the inversion. In the full sibs of animals recently collected from a natural population in Sweden it is shown that high acceptance rate and strong preference for large male size both co-segregate with the α form of the inversion, and that low acceptance rate and a weak preference for large size co-segregate with the β form of the inversion. Both sets of genes appear to be located in or near the αβ inversion. The heterogeneity between crosses suggests the natural population from which the animals were collected was polymorphic for behavioural genes on the β haplotype. Crosses involving animals that had been in laboratory culture for seven generations indicated that variation in female mating behaviour had been lost. Possible reasons for the apparent instability of such behaviour are discussed.

A phenotypic analysis was performed on two alleles at the pygmy locus which arose by insertional mutagenesis in transgenic mice. Similar to the spontaneous mutant pygmy, the adult insertional transgenic mutants are 40% of the size of wild-type litter-mates whereas adult heterozygotes are 80% of wild-type litter-mates. An analysis of the various organs revealed that, in general, there was a reduction in weight of each organ commensurate with the overall reduction in body size. However, two organs did not follow this pattern, the brain being disproportionately larger and the adrenals disproportionately smaller in the mutant mice. In addition, mini-mice have less adipose tissue than their wild-type or heterozygous litter-mates. A developmental analysis determined that mutants could first be identified on the basis of reduced body weight at day 15·5 of gestation. The small size is not due to a growth hormone deficiency so these mice differ from other known dwarf mouse mutants. Therefore they should provide insight into the growth hormone-resistant human dwarnsms and help in furthering our knowledge of mammalian growth and development.

A hypothesis has been tested that alterations in the molecule of histone H1 are capable of influencing quantitative traits of an organism. Two pairs of isogenic lines were constructed by selfing of plants kept heterozygous either for allelic variants of histone H1 subtype 1 (His1 gene) or for allelic combinations (haplotypes) of closely linked genes of H1 subtypes 3, 4, 5 and 6 (gene cluster His(2–6)). After 19 and 15 generations of selfing, respectively, expectation of the length of chromosome which remained heterozygous has comprised 2·6 cM near Hisl and 3·5 cM near His(2–6). The third pair of isogenic lines was obtained as a result of two successive intracluster cross-over events bordering the gene of the subtype 5 (His5). In each pair of isogenic lines there have been revealed some statistically significant differences between mean values of a number of quantitative traits.

Up to now, no case of spontaneous sex reversal has been described in the urodele amphibian Pleurodeles waltl reared at ambient temperature. However in offspring reared under laboratory conditions, males, females but also intersex individuals were obtained. The males, some females and the intersexes had the ZZ male genotype identified through a test performed with a sex-linked enzyme. The other females had the ZW female genotype. Using the animals of this particular strain, an offspring analysis was made on crosses between, respectively, ZZ males and ZW females, ZZ males and ZZ females, and ZZ intersexes and ZZ males or females. All these crosses gave ZZ males, ZZ females and ZZ intersexes. The spontaneous complete or partial sex reversal is inheritable, but the genetic mechanism of this inheritance has not yet been elucidated.

We develop a model to predict the increase in genetic variance of a quantitative character in a hybrid population produced by crossing two previously isolated populations of the same species. The increase in variance in the F2 hybrids, the ‘segregation variance’, is caused by differences in the average allelic effects at each locus and by linkage disequilibrium among loci. We focus on the case in which the character is additively based and the average value of the character does not differ in the two populations. In that case the predicted segregation variance depends strongly on what is assumed about the genetic basis of the character. If the genetic variance of the character in each population is attributable to loci with numerous alleles of small effect that are in moderate frequency, as in Lande's (1975) model, the segregation variance should increase linearly with time since the populations were isolated, at a rate determined by the inverse of the effective population size. If the genetic variance is attributable to loci with alleles in very low frequency, as in Turelli's (1984) house-of-cards model or in Barton's (1990) model of pleiotropic, deleterious alleles, then the segregation variance in the hybrid population increases at a much lower rate.

Quantitative variation in traits that change with age is important to both evolutionary biologists and breeders. We present three new methods for estimating the phenotypic and additive genetic covariance functions of a trait that changes with age, and illustrate them using data on daily lactation records from British Holstein—Friesian dairy cattle. First, a new technique is developed to fit a continuous covariance function to a covariance matrix. Secondly, this technique is used to estimate and correct for a bias that inflates estimates of phenotypic variances. Thirdly, we offer a numerical method for estimating the eigenvalues and eigenfunctions of covariance functions. Although the algorithms are moderately complex, they have been implemented in a software package that is made freely available.

Analysis of lactation shows the advantages of the new methods over earlier ones. Results suggest that phenotypic variances are inflated by as much as 39 % above the underlying covariance structure by measurement error and short term environmental effects. Analysis of additive genetic variation indicates that about 90 % of the additive genetic variation for lactation during the first 10 months is associated with an eigenfunction that corresponds to increased (or decreased) production at all ages. Genetic tradeoffs between early and late milk yield are seen in the second eigenfunction, but it accounts for less than 8 % of the additive variance. This illustrates that selection is expected to increase production throughout lactation.

Using the Ewens sampling distribution of selectively neutral alleles in a finite population, it is possible to develop an exact test of neutrality by finding the probability of each configuration with the same sample size and observed number of allelic classes. The exact test provides the probability of obtaining a configuration with the same or smaller probability as the observed configuration under the null hypothesis. The results from the exact test may be quite different from those from the Ewens—Watterson test based on the homozygosity in the sample. The advantages and disadvantages of using an exact test in this and other population genetic contexts are discussed.