Biology Topic 12: Evolution and Speciation

Evolution

the process through which the characteristics of species change and through which newspecies arise

For evolution to happen, the variation must be…

Heritable or passed down from parents to offspring

Heritable variation

When individuals differ in heritable traits

Heritable variation =

1) Different alleles exist in a population

2) Individuals have different combinations of alleles

Genes come in different versions called…

“Alleles”

Genetic variation comes from two sources:

1) mutations

2) sexual reproduction

A mutation is…

A random change in DNA. Can produce new alleles that never existed before. Usually not helpful.

In sexual reproduction, 2 individuals contribute DNA to offspring, produces new _____ of alleles

Combinations

Mechanism

A way something happens.

Mechanisms of evolution change _____ over generations

Populations

Natural selection

Caused by pressure from the environment

Genetic Drift

Loss of alleles as individuals migrate by random chance

Gene Flow

Flow of alleles as individuals migrate into or out of the population

Mutations have a very _____ effect on how common alleles are, so it really doesn’t change populations

Small

What does natural selection NOT do?

1) Doesn’t make new traits exist (the trait is already there, natural selection just makes it more common)

2) Doesn’t change individuals (it changes populations)

Helpful traits are called…

adaptations

The advantage of an individual’s adaptations is measured by biological________.

Fitness (reproductive success)

Fitness

a measure of how many offspring an            individual contributes to the next generation

Transitional fossil

Fossil showing how one type of animal (or plant) evolved into another

Examples of transitions:

1) ancient fish gave rise to walking animals

2) Whales evolved from land ancestors

Fossil

Impressions / remains of ancient organisms

Comparative anatomy

Comparing body structures between different species

Homologous structures

Structures in different species that were passed down from a common ancestor

Vestigial structures

Structures that functioned in an ancestor but no longer are used - leftover structures of earlier evolution

Molecular similarities

When DNA and proteins are the same between species

Species

Distinct type of organism. Body function, behavior, genetic makeup are also used to identity species. Often recognized on the basis of how they look.

Hybrid

Has parents of two different species. Occurs if species are similar enough.

Speciation

Process by which one species splits into two species

The two steps of speciation

1) populations become separated, gene flow stops

2) Separated populations become different through evolution and develop barriers in reproduction

Different species often have similar body structures that were passed down from a…

Common ancestor

Biological species concept

A group of populations whose members have the potential to interbreed in nature and produce fertile offspring

Reproductive barriers ________ species from each other genetically so there is no gene mixing (gene flow)

Isolate

Temporal Isolation

When 2 species breed at different times (e.g. one tree releases pollen in spring, another tree releases pollen in summer)

Behavioral Isolation

When different species have different courtship behavior

Hybrid offspring can’t __________

Reproduce

Extinction

When there are no longer individuals of a species left alive

What are the three factors that contribute to extinction?

Localized distribution, invasive species, and habitat loss

Localized distribution

When species only live in a small area

Invasive species

Can hurt native species by predation, competition, or being a pathogen / parasite.

Currently the 2nd leading cause of extinction. Brought by humans! -proliferated = “did well”

Habitat loss

Happens when habitats are changed in ways so that they no longer support species that lived there in the past. CURRENTLY THE LEADING CAUSE OF EXTINCTION.