Evolution & Natural Selection

Biological Evolution

change in the genetic makeup of a population over time. Individual organisms don’t evolve: populations do.

Microevolution

evolution occurring within populations; changes in allele frequency from
one generation to the next

Macroevolution

evolution occurring above the species level, including the origination,
diversification, and extinction of species over long periods of evolutionary time

Allele

Different forms of a gene

Allele Frequency

number of a particular allele in a population divided by the total number of alleles in the population.

Gene Pool

all of the alleles present in all individuals of a population or species

Population

A group of individuals of the same species that interbreed.

Ultimate Source

Mutations — random changes in DNA that introduce new alleles.

Other sources: Recombination during meiosis, sexual reproduction.

Evolution depends on variation;

without it, natural selection and adaptation cannot occur.

Hardy-Weinberg Equilibrium

Describes the genetics of a non-evolving population.

Unless acted upon by outside forces, allele and genotype frequencies in a population will not change from one generation to the next
p2 + 2pq + q2 = 1
p= frequency of the dominant allele
q= frequency of the recessive allele

Conditions for H-W Equilibrium

There can be no differences in the survival and
reproductive success of individuals (i.e. no natural
selection).

Populations must not be added to or subtracted
from by migration. (No gene flow)

There can be no mutation.

The population must be sufficiently large to
prevent sampling errors.

Individuals must mate at random

If not in H-W equilibrium:

The population is evolving.

Mechanisms of Evolution

Natural Selection

Mutation

Genetic Drift (random events)

Gene Flow (migration)

Nonrandom Mating

What is natural selection?

A process where individuals with advantageous traits have higher reproductive success

Define adaptation.

A trait that increases an organism’s fitness in its environment.

Why is natural selection the only mechanism that leads to adaptation?

Because it increases the frequency of beneficial traits that improve survival and reproduction.

How is artificial selection different from natural selection?

Artificial selection is human-directed; natural selection is driven by the environment.

What is sexual selection?

Selection for traits that increase mating success.

Contrast intrasexual and intersexual selection.

Intrasexual = competition within same sex; Intersexual = mate choice by opposite sex.

Name one non-adaptive mechanism of evolution.

Mutation, gene flow, nonrandom mating, or genetic drift.

What is genetic drift?

Random change in allele frequencies, especially in small populations.

What is the founder effect?

When a few individuals start a new population with different allele frequencies.

What is the bottleneck effect?

A sharp reduction in population size that alters allele frequencies randomly.

What is fixation?

When an allele becomes the only allele at its locus in a population.

What is binomial nomenclature?

A system of naming species with two Latin names: Genus + species (e.g., Homo sapiens).

List the taxonomic hierarchy from broadest to most specific.

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Biological

Can interbreed & produce fertile offspring.

Morphological

Based on appearance

Phylogenetic

Based on evolutionary history.

What is the biological species concept?

A species is a group of interbreeding natural populations that are reproductively isolated from others.

Give an example of a prezygotic isolating mechanism.

Behavioral, temporal, ecological, mechanical, or gametic isolation.

What is the difference between allopatric and sympatric speciation?

Allopatric = geographic separation;

Sympatric = same area, but reproductive isolation.