Biology

Evolution by natural selection occurs when a)______ leads to differential success in b)______ and c)_______.

Because of a)______, genetic variation is b)______ in populations.

True or False

Is lack of genetic variation is usually a good or bad thing?

Genetic variation provides the foundation for a)_____ when environmental conditions b)______.

Patterns of Natural Selection

I. Directional Selection

allele frequencies change in
a)_____direction
 Changes the b)______ of a trait
Tends to c)_____ the genetic diversity in populations by d)_____ one e)_____ over another.

Patterns of Natural Selection


An example of Directional Selection:

drug resistance in certain bacteria

Directional Selection can be a)_____ if environmental conditions warrant such a change.

An example of reversed directional selection: drop in temperature vs. decline in cliff swallow population
 Known as a)______ directional selection
 Can help b)_____ genetic variation in a population.

II. Stabilizing Selection


a)_____ extremes in a population are
b)_____ and the c)______ phenotype is favored

An example of Stabilizing selection:

What are the two consequences to stabilizing selection?

1. a)____ change in the b)______ of a trait over time.

What are the two consequences to stabilizing selection?

2. a)______ in the population is b)_____

III. Disruptive Selection

a)_____ extremes in a population are
b)_____ and the c)_____ phenotype is selected d)_____.

Disruptive selection is relatively a)____, but b)_______ in a population in which it occurs.

Disruptive selection plays a role in a)_____ – the generation of new b)_____.

II. Genetic Drift

Any a)____ in the b)______ in a population that is due to c)_____.

Genetic drift causes a)_____ to drift
b)_____ randomly over time.

a)______ can be simulated through the flipping of a coin.

Three Important Points about Genetic drift:

I. a)_____ with respect to fitness. Allele freq changes are not b)_______.

Three Important Points about Genetic drift:

II. Much a)_____ effect in b)_____ pops than in large ones.

Three Important Points about Genetic drift:

III. Can lead to the a)_____ or b)____ of alleles.

How do founder effects cause drift?

Drift occurs when a group of individuals a)______ to a new geographic area and establish a
b)______.

The cause of founder effects on drift:

If the new population is a)____, allele frequencies will likely be b)______ -this is the founder effect

How do population bottlenecks cause drift?

Sudden reduction in population size caused by stochastic events:

Bottle necks:

Remaining individuals likely have
a)_____ than the original pop.

III. Gene Flow

Refers to the a)_____between populations via b)______.

Gene Flow tends to a)_______ among populations. (lupine example)

Gene flow is a)_____ with respect to fitness.

During gene flow, movement of alleles between pops a)______ between them.

During gene flow, human migration across continents is a)______ in human populations.

IV. Mutation

Mutation occurs a)_______. Therefore,
b)______ of the Hardy-Weinberg model is almost certain to be violated

Effects of Mutation

I. Constantly a)____ into all pops at all loci.
o b) Increases_______ in pops
o Random with respect to c)_____.

True or false


Is mutation an important cause of evolutionary change?

Mutation a)______ often enough

Most mutations give rise to a)_____ that decrease b)_____.

Mutation as an Evolutionary Mechanism

Mutations happen a)____ to cause dramatic changes in b)______.

Mutation is an a)______mechanism compared with selection, genetic drift, and gene flow.

Mutation can play a role in a)____when the number of alleles is b)_____.

Mutation introduces a)______ into every individual in a population every generation

In sexually reproducing organisms,
a)_____ generates new combinations of alleles as well. Therefore, mutation restores b)_______.

What role does mutation play in evolutionary change?

Mutation was the a)______ in these populations.

The role of mutation in evolutionary change.

Competition experiments proved that
a)______ dramatically over time.

True or false.

Is mutation the ultimate source of genetic variability?

Without mutation, there is no a)_____ on which b)______ can work.

Although mutation rates are a)___for individual loci it may be high throughout entire b)_____.

Mutation becomes an evolutionary force when
 Considered a)_____entire genomes
 Combined with b)_____.

Nonrandom Mating


Inbreeding is a)______between b.______.

Inbreeding depression: loss of
a)____that takes place when b)_____.

Inbreeding depression occurs because the freq of a)_______ recessive alleles b)_____.

Does inbreeding cause evolution directly?

No

Inbreeding a)____ change allele frequencies

Inbreeding can speed the rate of a)____.