Lecture 5 Flashcards
Fisher, Haldane and Wright’s Neo - Darwinism
Continuous variation and Darwinian natural selection are completely consistent with Mendel’s Laws, demonstrating evolutionary significance of genetic diversity
3 Key Questions in Ecological and Evolutionary Genetics
- What forces influence GD patterns in populations?
- How can one measure the amount of GV in populations?
- How much and what types of genetic variation occur in populations?
5 Forces that Influence Patterns of Genetic Diversity and Evolution
- Mutation
- Recombination
- Genetic drift
- Gene flow
- Natural selection
Gene flow vs. genetic drift
Gene flow: movement of new alleles into an existing gene pool through immigration
Genetoc drift: random events that result in a different allele frequency: significant decrease or increase of a population size that result in more organisms with a particular trait surviving
How the 5 Processes Influence Genetic Diversity
Mutation, recombination and gene flow increase diversity
Genetic drift decrease diversity
Natural selection can do both
Metrics of Genetic Variation
Heterozygosity and polymorphism
Definition of Heterozygosity
Fraction of individuals that are heterozygous, average across gene loci
Definition of Polymorphism
Proportion of gene loci that have 2 or more alleles in the population; possible without heterozygosity
2 Modes of the Maintenance of Genetic Variation
- Mutation selection balance: less fit types reintroduced by mutation, followed by selection acting to remove them
- Selection maintaining variation: heterozygote advantage, frequency - dependent selection. Fitness varies in space or time
2 schools of thought on how much genetic variation occurs in natural populations
Morgan, Muller: classical: low heterozygosity and polymorphism, wild type is normal genotype, selection typically negative
Dobzhansky, Ford: balance: heterozygote advantage, high heterozygosity and polymorphism, selection favours diversity
Cytology Definition
Study of cells
What do evolutionary responses of continuous traits demonstrate?
Existence of heritable variation in fitness - related phenotypes
Responses to artificial selection demonstrate…
Abundant genetic variation exiss for polygenic quantitative traits
Allozyme gel electrophoresis
Different allelic forms of the same protein that undergo gel electrophoresis
Application of allozyme gel electrophoresis
Determinign the proportion of genes that are variable and measures the diversity of genes that encode enzymes and proteins
Monomorphic vs polymorphic genes on the gel electrophoresis
Monomorphic: single line
Polymorphic: more than one line with different spots on different coordinates
Advantages of Studies of Enzyme Polymorphism
- Many loci examined
- Used in nearly any organism
- Loci codominant, heterozygotes can be determined
- Variation examined close to DNA level
- Provides genetic marker loci for other studies
Selectively Neutral Variation
Different types do not differ in their fitness relative to each other; new mutations neither eliminated nor retained by selection
First Allozyme Studies
- Mutation seelction balance: less fit types maintained
- Selection maintaining variation: heterozygote advantage, frequency dependent selection
- Selectively neutral variation
The Kimura Neutral Theory
Most molecular variation may be selectively neutral
- Positive selection fixes beneficial mutations while negative selection eliminates detrimental mutations
Only ones left are neutral
Genetic Variation at the DNA Level
Direct inference of genetic differences, genetic code for genes can distinguish changes that alter protein from those that don’t
