Unit 9.2 Natural Selection

Define natural selection

The process in which individuals with advantageous inherited characteristics survive and reproduce more successfully; increasing the frequency of those characteristics over generations.

What are the three sources of genetic variation

Mutation; meiosis; and sexual reproduction.

How does mutation create genetic variation

Mutations change DNA sequences and can create new alleles.

How does meiosis create genetic variation

Crossing over and independent assortment produce new combinations of alleles in gametes.

How does sexual reproduction create genetic variation

Random fertilization combines alleles from two parents to produce genetically unique offspring.

Which sources of variation create new alleles and which create new combinations

Mutation creates new alleles; meiosis and sexual reproduction create new combinations of existing alleles.

Compare variation caused by mutation and sexual reproduction

Mutation creates new genetic information by changing DNA; sexual reproduction rearranges existing genetic information into new combinations.

Why can natural selection only occur when variation exists

Individuals must have different inherited characteristics for some to have a reproductive advantage over others.

Why do species produce more offspring than their environment can support

Overproduction increases the chance that some offspring will survive environmental challenges and reproduce.

What are two evolutionary benefits of overproduction of offspring

It increases the likelihood that some offspring survive; and provides variation for natural selection to act upon.

What is competition for resources

Competition occurs when individuals need the same limited resources such as food; water; space; shelter; and mates.

Define carrying capacity

The maximum population size an environment can sustainably support with its available resources.

What resources can limit population size

Food; water; space; shelter; nutrients; and available mates.

Compare direct and indirect competition

Direct competition involves individuals interacting to compete for resources; indirect competition occurs when individuals use the same limited resource without directly interacting.

Define selective pressure

An environmental factor that affects the survival and reproductive success of individuals with different characteristics.

What are biotic selective pressures

Factors caused by living organisms such as predators; competitors; parasites; pathogens; and availability of mates.

What are abiotic selective pressures

Nonliving environmental factors such as temperature; drought; pH; salinity; and sunlight.

Define density-independent factor

An environmental factor that affects populations regardless of their population density; such as natural disasters or extreme weather.

How do selective pressures affect variation in a population

They favor individuals with certain inherited characteristics; causing those individuals to reproduce more successfully and change allele frequencies over generations.

Define adaptation

An inherited characteristic that improves an organism's ability to survive and reproduce in its environment.

Define fitness in evolutionary biology

An individual's relative reproductive success; measured by its contribution of genes to future generations.

What happens to better-adapted individuals under natural selection

They are more likely to survive and reproduce; passing their advantageous inherited characteristics to offspring.

What happens to less-adapted individuals under natural selection

They are less likely to survive or reproduce successfully; so their inherited characteristics may decrease in frequency.

How does natural selection produce adaptations

Individuals with beneficial inherited variations reproduce more successfully; causing those characteristics to become more common over generations.

Distinguish between heritable and acquired characteristics

Heritable characteristics are genetically passed from parents to offspring; acquired characteristics develop during an individual's lifetime and generally are not inherited.

Why can natural selection only act on heritable characteristics

Only inherited genetic variations can be passed to offspring and cause evolutionary changes in future generations.

What are the two major mechanisms of sexual selection

Intrasexual selection; competition between individuals of the same sex; and intersexual selection; mate choice by the opposite sex.

What is intrasexual selection

Competition between members of the same sex for access to mates; such as male deer competing using antlers.

What is intersexual selection

Individuals choosing mates based on attractive characteristics; such as female birds choosing males with elaborate feathers.

Give examples of sexual selection involving coloration

Size

What selective pressures act on guppy coloration

Bright coloration attracts females but also makes males more visible to predators; creating opposing selective pressures.

Summarize John Endler's guppy experiment

Endler placed guppies in ponds with different predator conditions and observed changes in male coloration; demonstrating that predation and mate choice influence natural selection.

How did predatory fish affect guppy coloration

Predators favored less colorful males because they were harder to detect; reducing the frequency of bright coloration.

How did female mate choice affect guppy coloration

Females preferred brighter males; increasing their reproductive success and favoring bright coloration through sexual selection.

What was the independent variable in Endler's guppy experiment

The type of predator environment in each pond.

Why is natural selection not the same as artificial selection

Natural selection is driven by environmental selective pressures; artificial selection occurs when humans choose which organisms reproduce.

Explain the peppered moth case study

Before industrialization light-colored moths were better camouflaged on pale trees; pollution darkened tree surfaces and favored dark moths; their frequency increased through natural selection.

What is industrial melanism

An increase in the frequency of dark-colored forms of a species in industrially polluted environments due to natural selection.

Explain how antibiotic resistance evolves in bacteria

Random mutations can produce resistant bacteria; antibiotics act as a selective pressure by killing susceptible bacteria; resistant bacteria survive and reproduce; increasing resistance in the population.

Why is antibiotic resistance an example of natural selection rather than artificial selection

Antibiotics create an environmental selective pressure rather than humans deliberately choosing which bacteria reproduce; resistant bacteria survive and pass on resistance genes.

Explain how pesticide resistance evolves

Some insects have inherited resistance due to genetic variation; pesticides kill susceptible individuals; resistant individuals survive and reproduce; increasing resistance over generations.

Explain how finch beaks evolved on Daphne Major

During droughts hard seeds became more common; finches with larger stronger beaks could eat them more successfully; they survived and reproduced more; increasing the frequency of larger beaks.

What is a scientific model

A simplified representation of a real system or process used to explain; understand; or predict scientific phenomena.

Why do scientists use models

To simplify complex systems; test hypotheses; explain processes; and make predictions that may be difficult to investigate directly.