EVE100 Lecture 3 Inbreeding and Genetic Drift

Genetic Drift & Inbreeding Recap

Learning Objectives of Genetic Drift

• Explain how genetic drift changes allele frequencies through

random sampling.

• Predict how population size influences the strength of genetic

drift.

• Explain the effects of bottlenecks, founder events and effective

population size

What are the two most important forces that affect allele frequency changes in a population? Why?

Genetic Drift and Selection

Genetic Drift

Fluctuations in allele frequencies that occur by chance, particularly in small populations, because of sampling error

Selection

process where individuals with helpful, inheritable traits survive and reproduce more successfully than others, passing those advantages on to the next generations

What is Inbreeding Depression?

the production of offspring with reduced fertility from mating with closely related relatives

Mutations that affect fitness are majority _____ and _____.

Deleterious - harmful, disease causing

Recessive - only shows up when inheriting two copies of that specific gene

What does natural outbreeding populations contain?

Deleterious recessive alleles at low frequencies

What does inbreeding increase and do?

Inbreeding exposes more deleterious alleles as homozygotes ==> leads to reduced fitness

This is the primary cause of inbreeding depression

What does inbreeding affect?

affect all aspects of reproductive fitness, offspring numbers, juvennile survival, longevity, interbirth interval, mating ability, gamete quantity, and quality

Explain how genetic drift changes allele frequencies through random sampling

It changes through random sampling by chance, there is always a possibility for a bad trait to be permenant but the good trait will still be present within the population till chance.

finite populations pass on a random subset of gametes, creating a statistical sampling error that shifts gene proportions independently of adaptive fitness

Predict how population size influences the strength of genetic drift

The greater the population size, the weaker genetic drift is

The smaller the population size, the stronger genetic drift is

Explain the effects of bottlenecks, founder events and effective population size

TLDR how random chance alters genetic diversity

Bottleneck: some events reduce population size and eventually increase back in size

Founder events: loss in genetic variation when a new population is established by smaller group of individuals from the bigger group

Effective population size: The number of breeding individuals in an idealized population that would show the same amount of genetic drift as the real population.

What does a large population size mean?

little to no genetic drift

Genetic Drift

Fluctuations in allele frequencies that occur by chance (usually smaller populations) because of sample error

Are changes in genetic drift random?

True

Does genetic drift affect alleles that are strongly selected or weakly selected?

weakly selected

What is a binomially distributed random variable?

counts the number of successes in a fixed number of individual trials

What does genetic drift result from?

random sampling error

(higher when samples are small)

Rate of genetic drift is ____ in smaller populations

higher

Rate of genetic drift is ____ in larger populations

lower at a slow rate

What is the bottle neck effect?

Population and genetic diversity are reduced for at least one generation from an event (human activity or disaster)