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A total of 897 pigs were used in a study to investigate the relative effects of terminal sire genotype (lines Av.Bv. C), sex (castrate v. gilt), slaughter weight (80 v. 100 v. 220 kg), feeding regimen (ad libitum v. restricted, 0·82 ad libitum intake) and slaughter-house (HI v. H2 v. H3) on growth performance, carcass and meat quality characteristics and the eating quality offresh pig meat. Sire line A was a pure Duroc population, and B and C were European-type experimental lines where C contained Pietrain and B did not. In total, 26 sires from line A, 42 sires from line B, and 21 sires from line C were mated to females from the same crossbred dam line and progeny were reared under standard conditions to slaughter. Following slaughter and carcass evaluation, samples of longissimus dorsi were investigated for a range of meat quality and organoleptic characteristics. Line A produced fatter carcasses (C fat depths = 15·6 v. 24·0 v. 14·0 mm for lines A, B, and C, respectively, average s.e. 0·39) with higher killing-out proportions (g/kg) (790 v. 779 v. 786 respectively, average s.e. 1·4) and higher visible marbling, less tissue separation, firmer backfat, and juicier (3·81 v. 3·67 v. 3·72 respectively, average s.e. 0·044: on a scale 1 (extremely dry) to 8 (extremely juicy)) and more acceptable meat (4·54 v. 4·37 v. 4·42 respectively average s.e. 0·037: on a scale 1 (dislike extremely) to 8 (like extremely)) with a lower shear force (5·35 v. 5·78 v. 5·67 kg respectively, average s.e. 0·078) than lines B and C which were similar in most respects. Increases in slaughter weight were associated with a reduction in growth rate (785 v. 769 v. 725 glday for 80, 100 and 120 kg slaughter weight respectively, average s.e. 8·5), increases in backfat (Cfat = 13·3 v. 24·2 v. 26·3 mm respectively, average s.e. 0·34) and longissimus muscle area (34·6 v. 40·7 v. 44·6 cm2 respectively, average s.e. 0·59) and a deterioration in tenderness (4·72 v. 4·40 v. 3·95 respectively, average s.e. 0·062: on a scale 1 (extremely tough) to 8 (extremely tender) and overall acceptability (4·65 v. 4·44 v. 4·25 respectively, average s.e. 0·045) and an increase in shear force (5·37 v. 5·58 v. 5·87 kg respectively, average s.e. 0·085). Slaughter-house had a significant impact on pork odour scores but not on other organoleptic properties. Pigs reared under ad libitum feeding grew faster (840 v. 678 g/day respectively, average s.e. 3·7), were fatter (Cfat = 15·8 v. 23·2 mm respectively, s.e. 0·28), had lower carcass yields (780 v. 790 g/kg respectively, average s.e. 1) and produced more tender, juicier meat than those reared under restricted feeding. Differences between castrated males and gilts in growth and carcass trait were in line with other studies and there were no significant differences between the sexes for eating quality. There were relatively few significant interactions (P < 0·05) for eating quality traits and most of these involved slaughter-house and were for pork odour intensity, which are of limited practical significance. This suggests that the effects of sire genotype, slaughter weight and feeding regimen on eating quality identified in this study are likely to be additive.

SUMMARYFrom the available electrophoretic data, it is clear that haplodiploid insects have a much lower level of genetic variability than diploid insects, a difference that is only partially explained by the social structure of some haplodiploid species. The data comparing X-linked genes and autosomal genes in the same species is much more sparse and little can be inferred from it. This data is compared with theoretical analyses of X-linked genes and genes in haplodiploids. (The theoretical population genetics of X-linked genes and genes in haplodiploids are identical.) X-linked genes under directional selection will be lost or fixed more quickly than autosomal genes as selection acts more directly on X-linked genes and the effective population size is smaller. However, deleterious disease genes, maintained by mutation pressure, will give higher disease incidences at X-linked loci and hence rare mutants are easier to detect at X-linked loci. Considering the forces which can maintain balanced polymorphisms, there are much stronger restrictions on the fitness parameters at X-linked loci than at autosomal loci if genetic variability is to be maintained, and thus fewer polymorphic loci are to be expected on the X-chromosome and in haplodiploids. However, the mutation-random drift hypothesis also leads to the expectation of lower heterozygosity due to the decrease in effective population size. Thus the theoretical results fit in with the data but it is still subject to argument whether selection or mutation-random drift are maintaining most of the genetic variability at X-linked genes and genes in haplodiploids.

Aims/hypothesis. The aim of this study was to measure the heritability estimates for metabolic traits and the features of the insulin resistance syndrome in families with an increased genetic susceptibility to Type 2 diabetes. Methods. A total of 811 non-diabetic relatives from 278 pedigrees of northern European extraction in which there was a sib-pair with Type 2 diabetes were recruited and studied at the six Diabetes UK Warren Type 2 diabetes centres. Heritability estimates were calculated, allowing for key covariates (age, sex, BMI and recruitment centre). Values greater than 0.10 were considered statistically significant in comparison to zero. Results. Fasting glucose concentration and homeostasis model assessment of pancreatic beta cell function (HOMA %B) had the highest heritability estimates of 0.72 and 0.78 respectively. Heritability estimates for the features of the insulin resistance syndrome (BMI, WHR, systolic and diastolic blood pressure, serum lipids and homeostasis model assessment of insulin sensitivity [HOMA %S]) were also high. The heritability estimate for fasting glucose was markedly higher in the present study (0.77 vs 0.21 adjusted for age and sex; p<0.001) than in a comparable study of families from the same background population but with no increased susceptibility to diabetes. However, the estimates for the features of the insulin resistance syndrome were similar in the two studies. Conclusions/interpretation. In families with a high risk of Type 2 diabetes, the heritability estimates for fasting glucose, pancreatic beta cell function and the features of the insulin resistance syndrome were all high. The higher heritability estimate for pancreatic beta cell function suggests that this resource may be most effective when investigating genetic susceptibility to beta cell dysfunction.Keywords Heritability · Quantitative traits · Risk of Type 2 diabetes · Insulin resistance syndrome · Genetic susceptibility