Population Genetics: Drift, Mutation, Local Adaptation, and Speciation

A set of practice flashcards covering drift, mutation, local adaptation, speciation, gene flow, prezygotic isolation, Hardy-Weinberg assumptions, natural selection, and polygenic trait distributions as discussed in the lecture notes.

What happens to allele frequencies under random genetic drift over time, and why is it unlikely for two populations to follow the exact same path?

Allele frequencies fluctuate randomly (random walks); two independent populations rarely have exactly identical trajectories.

How does mutation affect divergence between populations compared to genetic drift?

Mutation introduces new alleles randomly and tends to drive divergence between populations over time.

In the stickleback example, what trait demonstrates local adaptation and potential divergence between populations?

The number of plates on the stickleback fish, which diverges due to local environmental differences (e.g., water clarity) across populations.

What is the relationship between the amount of divergence between populations and the likelihood of speciation?

The longer populations diverge, the more likely speciation is to occur due to accumulating genetic incompatibilities.

What happens when independently evolved alleles from two populations (A and B) are brought together in the same individual?

There can be negative interactions causing reduced viability or fertility, potentially involving many genes.

How does gene flow affect the process of speciation?

Gene flow homogenizes populations and can prevent speciation by mixing alleles between populations.

What are the two flavors of prezygotic isolation described in the notes?

Pre-mating isolation (the individuals don’t mate) and post-mating isolation (mating occurs but results in problems preventing a viable zygote or offspring).

What are the Hardy-Weinberg assumptions mentioned in the notes?

Infinite population size, no selection, no migration, and no mutation (with the implied random mating assumption in classic HW theory).

Under what condition does natural selection occur according to the notes?

When there is variation in traits that increases survival and reproduction, leading to changes in trait frequencies in the next generation.

What trait distribution in sticklebacks is used to illustrate how normal continuous distributions arise with multiple genes?

The distribution of plate numbers across individuals, a polygenic trait that produces a continuous, normal-like distribution.

Why do we expect continuous distributions for traits controlled by many genes?

Because many genes with additive effects contribute to the trait, creating a range of phenotypes rather than discrete categories.

What environmental factor is linked to the divergence observed in sticklebacks, illustrating local adaptation?

Environmental changes affecting water clarity (or similar conditions) that create different selective pressures across populations.