What is the Law of Large Numbers?
Actual frequencies mirror expected frequencies when sample sizes are very large. (Ex. the coin toss experiment; 1000 vs. 10 tosses)
What is Genetic Drift?
- In finite pops, all allele frequencies fluctuate over time, even in the absence of natural selection
- Some alleles are fixed others are lost and the fractions of heterozygotes in the pop. decreases over time
- Separate populations diverge in their allele frequencies.
What is the Wright - Fisher Model?
Just like HW, it’s a simple way to describe how gene versions (alleles) change in a population over generations by random chance, assuming a fixed population size and random mating.
What are the ways LD can happen?
1) Selection
2) the rate of genetic recombination
3) mutation rate
4) genetic drift
5) the system of mating
6) population structure
What is Observed vs. Expected Heterozygosity?
Observed heterozygosity is how many individuals actually have two different versions of a gene, while expected heterozygosity is how many you would expect to have two different versions based on the gene frequencies.
What is Effective Population size (Ne)?
the population that’s actually producing. (Ne is size of an ideal population that would experience the same amount of drift).
Abbreviations Ne and He
What is Population bottleneck and Founder Effect?
A bottleneck occurs when a disaster reduces population size, leaving a small, non-representative sample of survivors.
A founder effect happens when a few individuals establish a new, isolated population, resulting in unique allele frequencies
What is Leading Edge Expansion?
A form of drift via founder effects leading to reduced genetic diversity in the newly colonized area
What is Neutral Theory of Molecular Evolution?
Molecular Evolution looks at the genotype, not phenotype. Fine scale view to nucleotide changes over time, which push phenotypic changes.
What is Nearly Neutral Theory of Mol. Evolution?
Smaller populations have longer generations, smaller pops have higher sub rates due to drift. (The larger the organism, the smaller the population, the more drift).
Substitutions vs. Mutations
What are Pseudogenes?
“fake genes”
What is Positive vs. Purifying selection?
Purifying selection (negative selection) removes deleterious mutations to conserve functional sequences, while positive selection (Darwinian selection) drives the spread of advantageous mutations to promote new adaptations.
What are Molecular Clocks?
a technique in evolutionary biology that estimates the timing of species divergence by measuring the number of accumulated genetic mutations, assuming a relatively constant rate of change. (It kinda works).
Molecular clocks are useful when comparing a single locus over a short time for closely related organisms.
What is Coalescent Time - Recency of common… and what does 2N mean???
The number of generations that we must go back for a population to be reduced to two parental lineages. Turns out it equals about 2N (population size) generations.
- Population size is the largest factor in determining coalescent time.
What are Polygenic traits?
Polygenic traits show near continuous variation because they have additive genetic effects.
What are Additive genetic effects?
the cumulative, independent contribution of multiple genes or alleles to a single phenotypic trait.
- Skin color, hair color, height, eye color etc.
- Diabetes, Heart disease
What is Latent Variation?
Not new variation, but a new assortment of previously occurring Mendelian variation when multiple genes control “one” trait.
- Selection reveal latent variation
What is Epistasis?
Two or more alleles interact in non-additive ways
What is Haplotype vs. Genotype?
Genotype is the full set of genetic variants an individual has, while a haplotype is 2 genes that are not the same but on the same chromosome.
- Haplotype has to be in linkage equilibrium
What is Physical Linkage?
the proximity of two or more genes or genetic markers located on the same chromosome.
What is Linkage Disequilibrium (and the Coefficient of LD)?
is the non-random association of alleles at different loci in a given population. Loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is higher or lower than what would be expected if the loci were independent and associated randomly.
What is Genetic Hitchhiking?
occurs when a neutral or slightly deleterious gene increases in frequency because it is physically linked to a nearby beneficial gene undergoing strong positive selection.
