BIOL 105: Lecture 07 Genetic Drift

Flashcards about Genetic Drift

Evolution

A change in allele frequencies in a population over time

Random Process

Processes that can have different outcomes where we can not predict which outcome will occur for any given case

Genetic Drift

A change in allele frequencies caused by 'random sampling' in populations

Genetic Drift

The random change of allele frequencies from one generation to the next due to random sampling

Random Sampling

Any process that has the effect of randomly adding or subtracting fitness irrespective of genotype

Random Environmental Events

Natural disasters can kill individuals randomly, resources and mates can be randomly encountered or lost

Drift

Causes the loss of genetic diversity

Small Populations

The effects of genetic drift are more extreme in these

Census Size

The count of all the individuals in the population

Effective Population Size

The number of breeding individuals in an idealized population that would show the same amount of genetic drift as seen in the population being studied

Genetic Bottleneck

Occurs when a population is greatly reduced in size, which limits the genetic diversity of the species

Founder Effects

Occur when some individuals become isolated from a larger population

Heterozygosity

Genetic variation in a population can be quantified by this

Genetic Drift - Unbiased

The frequency of any allele is just as likely to go up as to go down (unlike selection)

Drifting causes genetic variability to be lost

Allele frequencies that fluctuate will eventually reach 0 or 1.

Fixation

Drift causes alleles to reach 100% even in the absence of all selection

Drift

Mutations with large fitness effects can easily overcome this

Genetic Drift and Selection

An allele evolves largely as if selection is not acting when s << 1/Ne, while it will evolve largely as if drift is not acting if s >> 1/Ne

Fixation

Drift will eventually cause the fixation (or loss) of all alleles

Fixation Probabilities

The probability that an allele will eventually fix is simply its current frequency

Pfix for a new mutation

Pfix= 1/(2N)