Introduction to Quantitative Genetics

Transcription

1 Introduction to Quantitative Genetics Fourth Edition D. S. Falconer Trudy F. C. Mackay

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3 PREFACE TO THE THIRD EDITION PREFACE TO THE FOURTH EDITION ACKNOWLEDGEMENTS INTRODUCTION ix x xi xiii f GENETIC CONSTITUTION OF A POPULATION 1 Frequencies of genes and genotypes 1 Mendelian variation in natural populations Causes of chang e Hardy-Weinberg equilibrium 5 The Hardy-Weinberg law Applications of the Hardy-Weinberg la w Mating frequencies and another proof of the Hardy-Weinberg la w Multiple alleles Sex-linked genes More than one locu s Non-random mating 19 Assortative mating Problems 20 2 CHANGES OF GENE FREQUENCY 23 Migration 23 Mutation 24 Non-recurrent mutation Recurrent mutatio n Selection 25 Change of gene frequency under selection Effectiveness of selection Number of generations required Average fitness and loa d Equilibria 3 4 Balance between mutation and selection Changes of equilibriu m Selection favouring heterozygotes Polymorphism 42 Problems 45 3 SMALL POPULATIONS: I. CHANGES OF GENE FREQUENCY UNDER SIMPLIFIED CONDITIONS 48 The idealized population 49 Sampling 5 1 Variance of gene frequency Fixation Genotype frequencie s Inbreeding 5 7 Inbreeding in the idealized population Variance of gene frequency Genotypefrequencies Problems 63

4 4 SMALL POPULATIONS : II. LESS SIMPLIFIE D CONDITIONS 65 Effective population size 6 5 Exclusion ofclosely related matings Different numbers ofmales and females Unequal numbers in successive generations Non-random distribution offamily size Minimal inbreeding Overlapping generations Mutation, migration, and selection 7 2 Non-recurrent neutral mutation Recurrent mutation and migratio n Selection Random drift in natural populations 7 6 Polymorphism 7 8 Neutral theory Problems SMALL POPULATIONS : III. PEDIGREE D POPULATIONS AND CLOSE INBREEDING 82 Pedigreed populations $ 2 The inbreeding coefficient ofan individual Coancestry or kinship Regular systems of inbreeding $ 8 Close inbreeding Fixation Repeated backcrosses Crosses and subsequent generations Mixed inbreeding and crossing Change of base: structured population Mutation Selection favourin g heterozygotes Problems CONTINUOUS VARIATION 100 Metric characters 102 Properties of metric characters 104 Problems VALUES AND MEANS 10 8 Population mean 10 9 Average effect 11 2 Breeding value 114 Dominance deviation 116 Interaction deviation 119 Problems VARIANCE 122 Components of variance ' 122 Components as proportions ofthe total Estimation of the degree of genetic determination, VG/Vp Genetic components of varianc e Additive and dominance variance Total genetic variance Interactio n variance Variance due to disequilibriu m Correlation and interaction between genotype and environment 13 1 Correlation Interaction

5 Environmental variance 134 Multiple measurements: repeatability Summary of variance partitioning 14 3 Problems RESEMBLANCE BETWEEN RELATIVES 14 5 Genetic covariance 14 6 Offspring and one parent Offspring and mid-parent Half sibs Full sib s Twins General Epistatic interactio n Environmental covariance 15 5 Phenotypic resemblance 157 Problems HERITABILITY 160 Estimation of heritability 16 3 Offspring parent regression Sib analysis Intra-sire regression of offspring on dam Combined estimate s Twins and human data 17 1 Assortative mating 174 Precision of estimates and design of experiments 177 Offspring parent regression Sib analyses Selection ofparents Problems SELECTION : I. THE RESPONSE AND ITS PREDICTION 184 Response to selection 18 5 Prediction ofresponse Selection differential and intensity ofselection Improvement ofresponse Measurement of response 194 Variability ofgeneration means Weighting the selection differentia l Realized heritability Maternal effects Change of gene frequency under artificial selection 199 Effects of selection on variance 20 1 Problems SELECTION : II. THE RESULTS OF EXPERIMENTS 208 Short-term results 208 Repeatability ofresponse Sampling variance Asymmetry ofresponse Long-term results 21 5 Selection limits Mutation Causes of selection limits Number of loci (effective factors) and standardized effects Problem SELECTION : III. INFORMATION FROM RELATIVES 228 Criteria for selection 229 Simple methods Prediction ofresponse Combined selectio n Relative merits ofthe methods

6 Index selection 240 Construction of an index Accuracy Response to selectio n Actual achievements Problems INBREEDING AND CROSSBREEDING : I. CHANGES OF MEAN VALUE 247 Inbreeding depression 247 The effect of selection Heterosis 253 Single crosse s Problems INBREEDING AND CROSSBREEDING : II. CHANGE S OF VARIANCE 263 Inbreeding 264 Redistribution of genetic variance Environmental variance Uniformity of inbred strains Mutation 269 Subline divergenc e Crossing 27 2 Variance between crosses Combining ability Problems INBREEDING AND CROSSBREEDING : III. APPLICATIONS 281 Selection for combining ability Three-way and four-way crosses ; backcrosses Reciprocal recurrent selection Overdominanc e Naturally self-fertilizing plants Problems SCALE 290 Distribution and variance Interactions Conclusions Problems THRESHOLD CHARACTERS 29 9 Liability and threshold Two classes, one threshold Adequacy of th e liability model Scale relationships Three classes, two threshold s Selection for threshold characters Problems CORRELATED CHARACTERS 312 Genetic and environmental correlations 312 Estimation of the genetic correlatio n Correlated response to selection 31 7 Indirect selection Genotype-environment interaction 321

7 Index selection 32 5 Construction of the index Response Effect of selection on geneti c correlations Problems METRIC CHARACTERS UNDER NATURAL SELECTION 33 5 Natural selection 33 5 Fitness and its components Relationships between metric characters and fitness 33 7 `Fitness profiles ' Responses to natural selection 33 9 Fitness Correlated responses Strength of selectio n Equilibrium populations 34 2 Fitness Major components Characters with intermediate optim a Characters with minimum fitness of intermediates Neutral characters Origin of variation by mutation 34 8 Mutational variance Maintenance of genetic variation 35 1 Balance between neutral mutation and random drift Mutation-selection balanc e Problems QUANTITATIVE TRAIT LOCI 356 Major genes 356 Methods of detection Methods for mapping QTLs 359 Marker loci QTL genotypes Single marker analysis Interva l mapping analysis Genetical and statistical considerations 366 Experimental design Multiple tests Maximum likelihood estimation Multiple QTLs Experimental results 370 Number of loci Gene effects Consistenc y From QTL to gene 37 5 Problem 37 7 APPENDIX TABLES 379 GLOSSARY OF SYMBOLS 38 1 Equivalence of symbols used by Mather and Jinks 38 3 SOLUTIONS OF PROBLEMS 38 5 REFERENCES 43 7 INDEX 459