SYSTEMS OF MATING. I. THE BIOMETRIC RELATIONS BETWEEN PARENT AND OFFSPRING

Index selection for genetic improvement of quantitative characters

This paper reviews the basic theory and summarizes various modifications of the selection index. The limitations of selection index are discussed in four parts: (1) changes of parameters due to selection. (2) sampling errors of parameter estimation. (3) evaluation of relative economic weights and (4) internal deterrents to index selection.

Inheritance of body weight and rate of gain in Japanese quail

The effects of hatch date, location and sex on the body weight and rate of gain in Coturnix coturnix japonica were examined. 2. The data conformed to a mixed and adjustments were made for the fixed effects sex, hatch date and location. Adjustment improved the precision of the estimates by reducing the error variances significantly. 3. Rearing equal numbers of birds from each family at different locations made the interactions negligible. 4. Weight gain was greater if illumination intensity up to 35 d was less. 5. Females were not heavier on the 1st day but were heavier on the 14th and 35th days than males. 6. Variance components and genetic parameters were estimated.

[Silvicultural treatments and their selection effects]

Selection can be defined in terms of its observable consequences as the non random differential reproduction of genotypes (Lerner 1958). In the forest stands we are selecting during the improvements-fellings and reproduction treatments the individuals surpassing in growth or in production of first-class timber. However the silvicultural treatments taken in forest stands guarantee a permanent increase of forest production only in such cases, if they have been taken with respect to the principles of directional (dynamic) selection. These principles require that the trees determined for further growing and for forest regeneration are selected by their hereditary properties, i.e. by their genotypes.For making this selection feasible, our study deals with the genetic parameters and gives some examples of the application of the response, the selection differential, the heritability in the narrow and in the broad sense, as well as of the genetic and genotypic gain. On the strength of this parameter we have the possibility to estimate the economic success of several silvicultural treatments in forest stands.The mentioned examples demonstrate that the selection measures of a higher intensity will be manifested in a higher selection differential, in a higher genetic and genotypic gain and that the mentioned measures show more distinct effects in the variable populations - in natural forest - than in the population characteristic by a smaller variability, e.g. in many uniform artificially established stands.The examples of influences of different selection on the genotypes composition of population prove that genetics instructs us to differentiate the different genotypes of the same species and gives us at the same time a new criterions for evaluating selectional treatments. These criterions from economic point of view is necessary to consider in silviculture as advantageous even for the reason that we can judge from these criterions the genetical composition of forest stands in the following generation, it means, within the scope of time for more than a human age.

Coefficients of inbreeding and homozygosity in recurrent selection: The case of m linked loci

Methods of calculating the coefficients of inbreeding and homozygosity in a finite population undergoing recurrent selection (self-select-intercross in succeeding generations) are investigated for the case of m linked loci and effective directional selection. These coefficients are derived in terms of vectors whose components reflect the various possible patterns of genes being identical at a given stage of the recurrent selection breeding program.For the case of two linked loci the progress of the panmictic index and/or the index of total heterozygosity through twenty-five cycles of recurrent selection is traced by means of computer-simulated populations ranging in sizes from ten through one hundred, assuming varying recombination probabilities, and assuming both minimum and maximum inbreeding selection patterns.Results indicate that the coefficient of relationship in the source population is extremely important in tracing the progress of the degree of inbreeding and/or total homozygosity, that linkage plays a major role in promoting heterozygosity in a recurrent selection system, and that careful intercrossing rather than random mating in alternate generations of the recurrent selection cycle is important in promoting maximum heterozygosity in the selected population. In the simulated populations the effect of small population sizes is observed and, in general, indications are that unless more than five complete recurrent cycles are contemplated, increasing the population size results in only relatively minor increases in panmixia, especially when linked loci are involved in the selected trait and when care is taken to avoid a maximum inbreeding selection pattern.

A note on parent-offspring correlation and inbreeding

For a diallelic autosomal character, the correlation between parental total score and offspring total score (known as the parent-offspring correlation) given by + √{s(1 + 3F)/[(s+ 1) +F(3s− 1)]}, is used here to estimateF, the constant which is commonly interpreted as coefficient of inbreeding. When the family records include varying number of children, a reasonably good estimate ofFis exhibited which agrees fairly with other available estimates.

Concordance in a twin population model

A twin population model is proposed, and two different definitions of the rate of concordance are investigated within the context of this model. It is found that the statistic formed from the ratio of the number of affected twins that come from concordant pairs to all affected twins has certain advantages over the traditional definition of the rate of concordance. This twin population model is extended to nontruncated sample of twins. The parameters of this situation are estimated. Finally, it is shown how these parameters relate to the two usual estimates of the proportion of DZ. twins in a twin population, and the efficiency of these methods is computed.

A new estimate of genetic load from inbreeding data

Inbreeding effect revealed as mortality and morbidity in general may be ascribed to deleterious mutations generally present at different loci of the ancestors common to each consanguineous mating. A new coefficient (E) is suggested to measure this effect. On the basis of this theory, a new method to estimate the load of mutations disclosed by inbreeding has been presented elsewhere, and is now extended. In this method, the load is estimated without introducing gene frequency notions. Genetic loads estimated through our method are in rather close agreement to those estimated through the classical theory of Morton, Crow and Muller (MCM).

Coefficients of inbreeding and homozygosity in recurrent selection: the one-locus case

For selection programs which can be represented by successive self-select-intercross cycles (such as recurrent selection or reciprocal recurrent selection) general recurrence formulae are developed for obtaining the coefficients of inbreeding and homozygosity in each cycle. The formula for the coefficient of inbreeding is a generalization of a result given by Sprague, et al. (1952). It is shown that the coefficient of parentage in the source population has a major effect on the coefficient of inbreeding in the following cycles as does the population size. The relationship of both types of coefficients and their importance in practical work are discussed.