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