scholarly journals MODIFICATIONS IN ESTIMATING THE NUMBER OF GENES FOR A QUANTITATIVE CHARACTER

Genetics ◽  
1986 ◽  
Vol 114 (2) ◽  
pp. 659-664
Author(s):  
C Clark Cockerham
Keyword(s):  
Least Squares ◽  
Genetic Variance ◽  
Quantitative Character ◽  
Gene Frequencies ◽  
Number Of Genes ◽  
Minimum Number

ABSTRACT In estimating the minimum number of genes contributing to a quantitative character, it is suggested that the squared difference between the means of the two parents be corrected for experimental variance and that the genetic variance stemming from differences in gene frequencies of the parents be estimated by least squares utilizing information on all entries.

scholarly journals How informative is Wright's estimator of the number of genes affecting a quantitative character?

Genetics ◽  
1990 ◽  
Vol 126 (1) ◽  
pp. 235-247 ◽  
Author(s):  
Z B Zeng ◽  
D Houle ◽  
C C Cockerham
Keyword(s):  
Genetic Variance ◽  
Estimation Procedure ◽  
Expected Value ◽  
Allele Frequencies ◽  
Quantitative Character ◽  
Base Population ◽  
Single Population ◽  
Number Of Genes ◽  
Selection Limit ◽  
The Difference

Abstract S. Wright suggested an estimator, m, of the number of loci, m, contributing to the difference in a quantitative character between two differentiated populations, which is calculated from the phenotypic means and variances in the two parental populations and their F1 and F2 hybrids. The same method can also be used to estimate m contributing to the genetic variance within a single population, by using divergent selection to create differentiated lines from the base population. In this paper we systematically examine the utility and problems of this technique under the influences of unequal allelic effects and initial allele frequencies, and linkage, which are known to lead m to underestimate m. In addition, we examine the effects of population size and selection intensity during the generations of selection. During selection, the estimator m rapidly approaches its expected value at the selection limit. With reasonable assumptions about unequal allelic effects and initial allele frequencies, the expected value of m without linkage is likely to be on the order of one-third of the number of genes. The estimates suffer most seriously from linkage. The practical maximum expectation of m is just about the number of chromosomes, considerably less than the "recombination index" which has been assumed to be the upper limit. The estimates are also associated with large sampling variances. An estimator of the variance of m derived by R. Lande substantially underestimates the actual variance. Modifications to the method can ameliorate some of the problems. These include using F3 or later generation variances or the genetic variance in the base population, and replicating the experiments and estimation procedure. However, even in the best of circumstances, information from m is very limited and can be misleading.

THE MINIMUM NUMBER OF GENES CONTRIBUTING TO QUANTITATIVE VARIATION BETWEEN AND WITHIN POPULATIONS

Genetics ◽  
1981 ◽  
Vol 99 (3-4) ◽  
pp. 541-553
Author(s):  
Russell Lande
Keyword(s):  
Genetic Factors ◽  
Inbred Lines ◽  
Quantitative Character ◽  
Standard Errors ◽  
Large Samples ◽  
Evolutionary Changes ◽  
Number Of Genes ◽  
Minimum Number ◽  
The Difference ◽  
Two Populations

ABSTRACT A procedure is outlined for estimating the minimum number of freely segregating genetic factors, nE,contributing to the difference in a quantitative character between two populations that have diverged by artificial or natural selection. If certain simple criteria are satisfied approximately on an appropriate scale of measurement, nEcan be estimated by comparing the phenotypic means and variances in the two parental populations and in their F1 and F2 hybrids (and backcrosses). This generalizes the method of WRIGHtTo genetically heterogeneous (or wild) parental populations, as well as inbred lines. Standard errors of the estimates are derived for large samples. The minimum number of genes involved in producing a large difference between populations in a quantitative trait is typically estimated to be about 5 or IO, with occasional values up to 20. This strongly supports the neo-Darwinian theory that large evolutionary changes usually occur by the accumulation of multiple genetic factors with relatively small effects.

scholarly journals Quantitative genetic variability maintained by mutation-stabilizing selection balance: sampling variation and response to subsequent directional selection

1989 ◽  
Vol 54 (1) ◽  
pp. 45-58 ◽  
Author(s):  
Peter D. Keightley ◽  
William G. Hill
Keyword(s):  
Genetic Variance ◽  
Directional Selection ◽  
Quantitative Character ◽  
Stabilizing Selection ◽  
Effective Population ◽  
Selection Responses ◽  
Quantitative Genetic ◽  
Before And After ◽  
Cage Population ◽  
Selection Of

SummaryA model of genetic variation of a quantitative character subject to the simultaneous effects of mutation, selection and drift is investigated. Predictions are obtained for the variance of the genetic variance among independent lines at equilibrium with stabilizing selection. These indicate that the coefficient of variation of the genetic variance among lines is relatively insensitive to the strength of stabilizing selection on the character. The effects on the genetic variance of a change of mode of selection from stabilizing to directional selection are investigated. This is intended to model directional selection of a character in a sample of individuals from a natural or long-established cage population. The pattern of change of variance from directional selection is strongly influenced by the strengths of selection at individual loci in relation to effective population size before and after the change of regime. Patterns of change of variance and selection responses from Monte Carlo simulation are compared to selection responses observed in experiments. These indicate that changes in variance with directional selection are not very different from those due to drift alone in the experiments, and do not necessarily give information on the presence of stabilizing selection or its strength.

ESTIMATION OF THE NUMBER OF GENES IN DOUBLED HAPLOID POPULATIONS OF BARLEY (HORDEUM VULGARE)

1982 ◽  
Vol 24 (3) ◽  
pp. 337-341 ◽  
Author(s):  
T. M. Choo ◽  
E. Reinbergs
Keyword(s):  
Hordeum Vulgare ◽  
Doubled Haploid ◽  
Doubled Haploids ◽  
Heading Date ◽  
Quantitative Character ◽  
Genotypic Variance ◽  
Hordeum Vulgare L ◽  
Sample Mean ◽  
Single Cross ◽  
Number Of Genes

It was shown that the number of segregating genes affecting a quantitative character in a single cross can be estimated by dividing the square of the deviation of the most extreme doubled haploid from the sample mean by the genotypic variance of doubled haploids. The number of segregating genes was estimated for three characters in four crosses of barley (Hordeum vulgare L.). It was found that the number of segregating genes for grain yield, heading date, and plant height ranged from 5 to 11, 6 to 9, and 4 to 13, respectively.

scholarly journals Using known QTLs to detect directional epistatic interactions

2012 ◽  
Vol 94 (1) ◽  
pp. 39-48 ◽  
Author(s):  
MONTGOMERY SLATKIN ◽  
MARK KIRKPATRICK
Keyword(s):  
Genetic Variance ◽  
Additive Model ◽  
Quantitative Character ◽  
Gene Interactions ◽  
Ratio Test ◽  
Linkage Equilibrium ◽  
Response To Selection ◽  
Epistatic Interactions ◽  
New Strategy ◽  
Trait Locus

SummaryEpistasis plays important roles in evolution, for example in the evolution of recombination, but each of the current methods to study epistasis has limitations. Here, we propose a new strategy. If a quantitative trait locus (QTL) affecting a quantitative character has been identified, individuals who have the same genotype at that QTL can be regarded as comprising a subpopulation whose response to selection depends in part on interactions with other loci affecting the character. We define the marginal differences to be the differences in the average phenotypes of individuals with different genotypes of that QTL. We show that the response of the marginal differences to directional selection on the quantitative character depends on epistatic gene interactions. For a model with no interactions, the marginal differences do not differ on average from their starting values once linkage equilibrium has been re-established. If there is directional epistasis, meaning that interactions between the QTL and other loci tend to increase or decrease the character more than under an additive model, then the marginal differences will tend to increase or decrease accordingly when larger values of the character are selected for. We develop a likelihood ratio test for significant changes in the marginal differences and show that it has some power to detect directional epistasis for realistic sample sizes. We also show that epistatic interactions which affect the evolution of the marginal differences do not necessarily result in a substantial epistatic component of the genetic variance.

scholarly journals INTERACTION BETWEEN NATURAL SELECTION FOR HETEROZYGOTES AND DIRECTIONAL SELECTION

Genetics ◽  
1974 ◽  
Vol 76 (1) ◽  
pp. 163-168
Author(s):  
Margrith Wehrli Verghese
Keyword(s):  
Natural Selection ◽  
First Generation ◽  
Genetic Variance ◽  
Selection Response ◽  
Directional Selection ◽  
Simple Function ◽  
Small Populations ◽  
Gene Frequencies ◽  
Selection For

ABSTRACT When directional selection for an additively inherited trait is opposed by natural selection favoring heterozygous genotypes a selection plateau may be reached where genetic variance is present. The amount of response when this plateau is reached is a simple function of the selection response in the first generation and the intensity of natural selection. When selection is practiced in small populations, the sizes of the initial equilibrium gene frequencies are at least as important as the intensity of natural selection in determining the probability of fixing desirable alleles.

scholarly journals Predicting the range of inbreeding depression of inbred lines in cross-pollinated populations

1997 ◽  
Vol 20 (1) ◽  
pp. 35-39 ◽  
Author(s):  
C.L. Souza Jr. ◽  
J.S.C. Fernandes
Keyword(s):  
Grain Yield ◽  
Plant Height ◽  
Inbreeding Depression ◽  
Genetic Variance ◽  
Inbred Lines ◽  
Gene Frequencies ◽  
Mating Design ◽  
Inbreeding Coefficients ◽  
Maize Population ◽  
Two Generations

The objectives of this paper were to derive the genetic variance of inbreeding depression (<img SRC="Image482.gif" WIDTH="48" HEIGHT="33"> ) and to predict the range of inbreeding depression (RID) in cross-pollinated populations. The variance of inbreeding depression is a function of the genetic variances related to dominance effects (<img SRC="Image483.gif" WIDTH="31" HEIGHT="33">, D2, and <img SRC="Image484.gif" WIDTH="21" HEIGHT="25">), and of the inbreeding coefficients of the two generations in which inbreeding depression is measured (Ft and Fg). The results showed that the higher the level of dominance of a trait, the higher the variance of inbreeding depression. The magnitudes of <img SRC="Image485.gif" WIDTH="48" HEIGHT="33">were expected to be lower in improved (mean gene frequencies = <img SRC="Image486.gif" WIDTH="16" HEIGHT="25">> 0.6) and in unimproved (<img SRC="Image487.gif" WIDTH="16" HEIGHT="25"> < 0.4) populations, than in composite populations (<img SRC="Image487.gif" WIDTH="16" HEIGHT="25"> <FONT FACE="Symbol">»</font> 0.5). Data from a maize population used to illustrate the study showed that the range of inbreeding depression in the S<FONT FACE="Symbol">¥</font> generation of selfing was from 48.7% to 85.3% for grain yield, and from 13.9% to 24.5% for plant height. A mating design outlined to estimate the genetic variance of inbreeding depression, the range of inbreeding depression, and of the range of inbred lines is presented.

scholarly journals Inheritance of Antioxidant Activity and its Association with Seedcoat Color in Cowpea

2005 ◽  
Vol 130 (3) ◽  
pp. 386-391 ◽  
Author(s):  
M. Ndambe Nzaramba ◽  
Anna L. Hale ◽  
Douglas C. Scheuring ◽  
J. Creighton Miller
Keyword(s):  
Antioxidant Activity ◽  
Combining Ability ◽  
Heritability Estimate ◽  
Maternal Parent ◽  
Five Factors ◽  
Diallel Mating Design ◽  
Dpph Method ◽  
Number Of Genes ◽  
Ability Tests ◽  
Minimum Number

The inheritance of antioxidant activity (AOA) and its association with seedcoat color was investigated in cowpea [Vigna unguiculata (L.) Walp.]. Four advanced cowpea lines, ARK95-356 (black seedcoat) and ARK98-348 (red seedcoat), which were high (H) in AOA, and ARK96-918 (cream seedcoat) and LA92-180 (cream seedcoat), which were low (L) in AOA, were selected from the 2002 Regional Southernpea Cooperative Trials. They were crossed in a complete diallel mating design, generating F1, F1′ (1st generation and 1st generation reciprocal cross, respectively), F2, F2′ (2nd generations from F1, F1′), BC1, and BC2 (backcrosses to parents 1 and 2, respectively) populations. Individual seeds were ground and samples were extracted in methanol and analyzed for AOA using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Combining ability tests using Griffing's Method I Model I indicated presence of highly significant general combining ability (GCA), specific combining ability (SCA), and reciprocal (RE) and maternal (MAT) effects, with pigmented lines exhibiting positive GCA and MAT, while nonpigmented lines exhibited negative GCA and MAT. AOA in the F1 was not significantly different from the maternal parent, with seedcoat color also resembling the maternal parent. Segregation for seedcoat color was observed in the F2 and F2′. Additive, dominance, and epistatic effects were significant. The broad sense heritability estimate was 0.87. Minimum number of genes responsible for AOA was estimated at five. Factors governing high AOA appeared to be the same as those responsible for seedcoat color, with apparent pleiotropic effects. In conclusion, breeding for high AOA in cowpea is possible using highly pigmented parental lines.

Sign in / Sign up

Export Citation Format

Share Document