Evolution & HW Theory

Natural selection

The process that changes allele frequencies when certain heritable traits are associated with different levels of reproductive success.

Biological Evolution

A change in allele frequencies in a population over time

Directional Selection

Natural selection that favors an extreme phenotype.

Stabilizing Selection

Natural selection that favors the average phenotype in the population and acts against extreme phenotypes.

Adaptation

A heritable trait that increases fitness in a particular environment associated with high fitness.

Theory

An explanation or set of hypotheses that attempt to explain a large and pervasive phenomenon, meaning they that tie together a large suite of observations about how the natural world works.

Fitness

The ability to produce viable offspring.

Mutation

Any change in the base sequence of DNA, and thus a change in genetic information. Introduces new alleles (genome) into population.

What is gene flow?

An evolutionary process that changes allele frequencies through the movement of individuals and their alleles from one population to another.

What effect does gene flow have on allele frequencies among populations?

It homogenizes allele frequencies among populations.

How does natural selection effect genetic variation?

Reduces genetic variation by eliminating alleles which can decrease fitness. BUT ALSO... increases fitness and leads to adaptation.

Genetic Drift

Randomly impacts fitness —alleles increase or decrease in frequency just due to luck (sampling effects). Reduces genetic variation.

Fixation

When genetic variation is reduced due to genetic drift. Alleles are lost in small populations.

Null Model

A model that predicts the data you should expect to see if a process is not working—meaning, when a particular causative agent is not impacting the situation.

What is the Hardy-Weinberg Principle?

A null model stating that allele frequencies will not change from one generation to the next under certain conditions.

What conditions must be met for the Hardy-Weinberg Principle to hold?

No selection, drift, gene flow, or mutation, and random mating with respect to the gene in question.

What are the genotype frequencies in the Hardy-Weinberg Principle?

The proportions are p², 2pq, and q².

What do p and q represent in the Hardy-Weinberg Principle?

p and q are the frequencies of two alleles at a gene.

Assortive Mating

Mate choice based on similarities or dissimilarities in phenotype. Evolutionary mechanism does not change allele frequencies, but changes genotype frequencies by increasing the proportion of homozygotes in the next generation?

What is a gene pool?

A concept used in predicting the results from random matings among all individuals in a population.

How does a gene pool function in reproduction?

It supposes that all gametes are tossed into a 'pool' and then drawn out at random to produce offspring.

inbreeding depression

lowered fitness due to the increased prevalence of homozygous recessive genotypes with deleterious effects

Extinction vortex

In some genetically isolated populations, a self-reinforcing cycle that lowers fitness and population size.

Anthropocene

A proposed interval in Earth's history where environments and species are undergoing massive and widespread change due to human activities.

You are studying a gene which has two alleles, A and a. You determine that in a population of snails, 34% of all alleles of this gene are a. This number (34%, or 0.34) represents the Blank______.

allele frequency of a

Blending Inheritance Theory

Offspring were expected to be phenotypically intermediate relative to their parents.

Processes that cause change in allele frequencies in a population.

• Gene flow

• Natural selection

• Mutations

• Nonrandom Mating

• Genetic drift

Allele Frequency

The number of copies of an allele in a population divided by the total number of all alleles for that gene in a population is the

New mutations are not a major factor affecting the allele frequencies in a population because

the rate at which new mutations occur is low

In small populations, advantageous alleles may be lost, and/or harmful alleles may increase in frequency, due to …

genetic drift