Selection with Partial Selfing. I. Mass Selection

The expected responses to mass selection carried out before or after reproduction in a population whose members all have a fixed probability of self pollination (s) are formulated using covariances of relatives and their component quadratic functions for a model with arbitrary additive and dominance effects. The response measured in the first generation offspring after selection (immediate gain) can differ from that retained when the population has regained equilibrium (permanent gain). The population mean behaves in a predictable manner during the return to equilibrium, and its value at any time can be predicted from earlier generations. The permanent gain from selection after reproduction is always (1 + s)/2 times as large as that from selection before reproduction, but the relationship of the immediate gains depends on the genetic model assumed. Numerical analysis applied to a model with two alleles per locus and varying allele frequencies, dominance ratios and numbers of loci showed that the proportion of the immediate gain retained at equilibrium was reduced with the large inbreeding depression associated with increasing dominance levels and numbers of loci and was generally lower for selection after reproduction than before. In the absence of information as to the magnitude of genetic variances and inbreeding depression in species reproducing by partial selfing, the importance of this phenomenon is unknown.     

动物的生境选择

动物的生境选择颜忠诚陈永林（中国科学院动物研究所,北京１０００８０）ＨａｂｉｔａｔＳｅｌｅｃｔｉｏｎｉｎＡｎｉｍａｌｓ．ＹａｎＺｈｏｎｇｃｈｅｎｇ,ＣｈｅｎＹｏｎｇｌｉｎ（ＩｎｓｔｉｔｕｔｅｏｆＺｏｏｌｏｇｙ,ＡｃａｄｅｍｉａＳｉｎｉｃａ,Ｂｅｉｊｉ...     

Selection in Finite Populations with Multiple Alleles. III. Genetic Divergence with Centripetal Selection and Mutation

Natural selection for an intermediate level of gene or enzyme activity has been shown to lead to a high frequency of heterotic polymorphisms in populations subject to mutation and random genetic drift. The model assumes a symmetrical spectrum of mutational variation, with the majority of variants having only minor effects on the probability of survival. Each mutational event produces a variant which is novel to the population. Allelic effects are assumed to be additive on the scale of enzyme activity, heterosis arising whenever a heterozygote has a mean level of activity closer to optimal than that of other genotypes in the population.-A new measure of genetic divergence between populations is proposed, which is readily interpreted genetically, and increases approximately linearly with time under centripetal selection, drift and mutation. The parameter is closely related to the rate of accumulation of mutational changes in a cistron over an evolutionary time span.-A survey of published data concerning polymorphic loci in man and Drosophila suggests than an alternative model, based on the superiority of hybrid molecules, is not of general importance. Thirteen loci giving rise to hybrid zones on electrophoresis have a mean heterozygote frequency of 0.22 +/-.06, compared with a value of 0.23 +/-.04 for 16 loci classified as producing no hybrid enzyme.     

The affected sib method. III. Selection and recombination.

The affected sib-pair method has been used to investigate the mode of inheritance, and to estimate the "disease" allele frequency, for a number of HLA-associated diseases. One of the assumptions of the original sib-pair method is that the disease confers no selective disadvantage on affected individuals. This is obviously not the situation for most diseases. We have determined the expected HLA haplotype-sharing distribution among affected sib-pairs when selection against individuals with the disease is taken into account. We have shown that if the mode of inheritance of the selectively disadvantageous disease is recessive or additive, the original affected sib-pair analysis, ignoring selection, still estimates the true mode of inheritance, but usually yields an underestimate of the "disease" allele frequency. For intermediate and dominant models of disease predisposition, both the estimates of the degree of penetrance of the "disease" genotypes, and the "disease" allele frequency, are altered if selection is ignored in the analysis. Similarly, allowing for recombination between the "disease" locus and the HLA region does not affect the determination of the mode of inheritance of the disease if it is recessive or additive; in other cases, however, the estimate of the mode of inheritance is affected. The "disease" allele frequency is overestimated when nonzero recombination is ignored for all the modes of inheritance that have been studied.     

Stabilizing and Disruptive Selection on a Mutant Character in Drosophila. IV. Selection on Sensitivity to Temperature

Individual selection on temperature sensitivity was applied to the relative length of the 4th vein of the mutant ci^D-G in four selection lines according to different selection schemes indicated in Figure 1. These selection systems include, besides the selection on temperature, disruptive selection. In all lines the disruptive component causes an increase of the phenotypic variance, but there are large differences in its composition. The selection changed temperature sensitivity in the expected direction in all lines. In one line (C-D^-) however, the change in temperature sensitivity and the increase in variance were only small because the disruptive component and the canalizing component of the selection scheme restricted each others' effect. The results are discussed in relation to earlier results obtained by disruptive selection at one temperature.     

Selection and fitness in bacteriocin-producing bacteria.

Bacteriocins are proteinaceous anticompetitor molecules produced by bacteria against closely related species. A number of theoretical models have been used to explain experimental data that indicate high polymorphisms among bacteriocins and a frequency-dependent nature of selection for bacteriocin-producing strains. The majority of these experimental data were, however, obtained from investigations into the colicin group of bacteriocins produced by Gram-negative bacteria. The conclusions drawn from these models have been extrapolated to other bacteriocins and allelopathic compounds in general. Examination of more recent experimental investigations into the bacteriocins of Gram-positive bacteria indicate a lower degree of polymorphism and a less frequency dependent mode of selection among these strains them among the colicin-producing strains. Here we examine these contradictions in the light of the assumptions and conclusions of the theoretical models and reported data. We show that fitness costs as indicated by decreased relative maximum growth rate associated with bacteriocin production may be much lower in many cases than is assumed in the present models. A lower fitness cost associated with bacteriocin production adequately explains the newer data from Gram-positive bacteria cited here, and indicates that extrapolation of existing models to all bacteriocins and other allelopathic compounds is not appropriate.     

Selection of representative protein data sets.

The Protein Data Bank currently contains about 600 data sets of three-dimensional protein coordinates determined by X-ray crystallography or NMR. There is considerable redundancy in the data base, as many protein pairs are identical or very similar in sequence. However, statistical analyses of protein sequence-structure relations require nonredundant data. We have developed two algorithms to extract from the data base representative sets of protein chains with maximum coverage and minimum redundancy. The first algorithm focuses on optimizing a particular property of the selected proteins and works by successive selection of proteins from an ordered list and exclusion of all neighbors of each selected protein. The other algorithm aims at maximizing the size of the selected set and works by successive thinning out of clusters of similar proteins. Both algorithms are generally applicable to other data bases in which criteria of similarity can be defined and relate to problems in graph theory. The largest nonredundant set extracted from the current release of the Protein Data Bank has 155 protein chains. In this set, no two proteins have sequence similarity higher than a certain cutoff (30% identical residues for aligned subsequences longer than 80 residues), yet all structurally unique protein families are represented. Periodically updated lists of representative data sets are available by electronic mail from the file server "netserv@embl-heidelberg.de." The selection may be useful in statistical approaches to protein folding as well as in the analysis and documentation of the known spectrum of three-dimensional protein structures.     

Selection with Gene-Cytoplasm Interactions. II. Maintenance of Gynodioecy

Gynodioecy is apparently frequently inherited through gene-cytoplasm interactions. General conditions for the protectedness of gene-cytoplasm polymorphisms for a biallelic model with two cytoplasm types were obtained previously, and these are applied to seven special cases of gene-cytoplasm interactions controlling gynodioecy and involving dominance. It is assumed that nuclear polymorphisms cannot be maintained in one cytoplasm type only. It is held that pure cytoplasmic inheritance of gynodioecy without nuclear interactions is unlikely, and it is shown that gynodioecy with gene-cytoplasm interactions is easier to establish than purely nuclear gynodioecy, for monogenic biallelic dominant or recessive inheritance. For three special cases, a resource-allocation model with simple assumptions always leads to conditions for protectedness of gynodioecy.