변이 (Variation)

1. Nature and Cause of Varia-tion

2. Evolutionary Significance of Variation

1. Nature and Cause of Variation

• Study of Variation within and among individuals, among populations, and among species

• 자연선택 , 표현형 형질 , 유전자 또는 환경에 따른 변이 정도 , 다음 세대로의 유전 정도

Modes of Expression of Variation

• Discrete Traits• Quantitative Traits• Threshold Traits• Sexual Dimorphic Traits

Discret

e Traits

Quanti-tative Traits

Mean, Variation

Variation

among popula-tion

s

Cause of Variation and their Evolu-tionary Consequences

• Variation within individuals

• Variation among individuals in ran-dom-mating, unstructured popula-tions

• Variation in structured populations – genotypes do not interact at random

Onto-genetic

Varia-tion

Ontogenic

Vari-ation

2. Evolutionary significance of Varia-tion

• Quantitative Traits genetic versus environmental

causes of phenotype variation

To-tal Pheno-type

Variation

R=h2S• R=h2S• R Response to selection (phenotype change between genera-

tion)• H heritability• S Selection differential (before and

after selection)

Genetic Variation Additive Genetic Variance Nonadditive Variance - Dominance variance - Cytoplasmic variance Epigenetic Variance Interaction of Nonadditive and Addi-

tive Genetic Variance

Table 2.1 Epistatic Interac-tion

Locus 2

Geno-types

Locus 1AA Aa aa

BB 11 10 9Bb 11 12 9bb 9 9 9

Table 2.2 Epistatic Interac-tion

Locus 2

Geno-types

Locus 1AA Aa aa

BB 6 2 1Bb 2 6 2bb 1 2 6

Interconversion of Nonadditive and Additive Genetic Variance

• Epistatic variation : Nonadditive Little direct part in response to selec-

tion• Epistatic/Alleic variation Loss : Con-

vert to Additive variation• Passing through the bottleneck : Ad-

ditive Genetic variation increase

Table 2.3 Schematic Exam-ple

Locus 2

Geno-types

Locus 1AA Aa aa

BB 8.0 6.0 4.0Bb 2.0 4.0 4.0bb 1.0 1.0 3.0

Genotype b loss makes BB only and additive variation

Environmental Variation• Abiotic Environmental Variation• Biotic Environmental Variation• Maternal Environmental Varia-

tion

Genotype X Environment Interaction

• Cannot be predictated on ths basis of each Genotype and Environment

• VP VG + VE , VP = VG x VE

• Diminishing heritability• Constraint evolutionary changes• Reduce potential response to selec-

tion

Genotype X Environmental Interaction