Biology Chapter 17: Evolution and Speciation

What is sexual selection?

When individuals select mates based on favorable heritable traits.

What is geographic isolation?

A form of reproductive isolation in which two populations are separated by geographic barriers causing the formation of two separate subspecies.

What is behavioral isolation?

A form of reproductive isolation in which two populations develop differences in courtship or other rituals that prevent them from breeding.

What is a species?

A group of similar organisms that can breed & produce fertile offspring.

What is a genetic drift?

A series of chance occurrences that can cause an allele to become more or less common in a population. It can be described as a random change in allele frequency.

What is the Founder Effect?

A situation in which allele frequencies change as a result of the migration of a small subgroup of a population.

What is genetic equilibrium?

A situation in which allele frequencies in a population remain the same due to no occurrences of evolution.

Describe single-gene traits.

A trait controlled by one gene that may have just two or three distinct phenotypes.

What is reproductive isolation?

By sexual selection, a separation of a species or population so that they can no longer interbreed & evolve into separate species.

What are the effects of natural selection on a population?

Different genotypes that have different fitness. This causes evolution to occur.

What are the effects of sexual reproduction on a population?

Gene shuffling which produces many gene combinations.

What are the effects of nonrandom mating on a population?

Genes for the traits selected for or against are not in equilibrium, causing evolution.

What are the effects of immigration and emigration on a population?

Individuals who join in a population bring new alleles into the gene pool. Individuals who leave may remove alleles from the gene pool. This disrupts genetic equilibrium. This can also introduce mutations.

What are the effects of disruptive selection?

It acts against individuals that are in the middle and can cause the curve to split and create two distinct phenotypes.

What determines the number of phenotypes for given trait?

It depends on how many genes control the trait.

What are the effects of Lateral Gene Transfer?

It increases genetic variation in any species that picks up the "new" genes.

What are the effects of stabilizing selection?

It keeps the center of the curve at its current position, but narrows the curve's range.

What does the Hardy-Weinberg principle state?

It states that allele frequencies in a population remain constant unless nonrandom mating, small population size, immigration or emigration, mutations, or natural selection occur, which causes evolution.

How does natural selection affect single-gene & polygenic traits?

Natural selection on single-gene traits can lead to changes in allele frequencies, causing changes in phenotype frequencies. Natural selection on polygenic traits can affect the relative fitness of phenotypes thereby producing directional, stabilizing, or disruptive selection.

Allele Frequency

Number of times an allele occurs in a gene pool compared to the goal number of alleles in that pool for the same gene.

How does natural selection affect genotypes by acting on phenotypes?

Phenotypes can benefit an organism and increase its survival in its environment. Indirectly, since genotypes determine phenotypes, natural selection can wipe out individuals carrying certain genotypes.

Which source of variation brings more diversity into a gene pool-mutation or sexual reproduction?

Sexual reproduction, because events such as crossing over and independent assortment in genetic recombination lead to more combinations of traits than mutations which affect a single trait at a time.

What is the current hypothesis about Galapagos finch speciation?

Speciation in Galapagos finches occurred by founding of a new population, geographic isolation, changes in the new population's gene pool, and behavioral isolation, which lead to ecological competition.

What is speciation?

The formation of a new species.

What is Lateral Gene Transfer and when does it occur?

The passing of genes from one organism to another that isn't an offspring. It occurs between or organisms of the same or different species, often in prokaryotes such as bacteria.

What are the effects of directional selection?

The range of phenotypes shifts b/c some individuals are more successful at surviving & reproducing than others.

What is fitness?

The success of genes passed on to the next generation.

What are the effects of mutations on a population?

They change allele frequencies causing evolution to occur.

What effect do mutations have on phenotypes?

They may or may not affect fitness. Some can lower fitness and some can improve.

Describe polygenic traits.

Traits controlled by two or more genes and have many possible genotypes and even more phenotypes. Phenotypes are not clearly distinct from one another.

What is directional selection?

When individuals at one end of the curve have higher fitness than individuals in the middle or at the end of the curve.

What is disruptive selection?

When individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve.

What is stabilizing selection?

When individuals near the center of the curve have higher fitness than individuals on either end.

Most heritable differences are due too...

genetic recombination during sexual reproduction (not mutation)

What are types of reproductive isolation?

1. Behavioral isolation 2. Geographic isolation 3. Temporal isolation

In what ways are genes recombined?

1. Crossing Over 2. Independent Assortment

What are some sources of genetic variation?

1. Mutation 2. Genetic recombination during sexual reproduction 3. Lateral gene transfer

What conditions are required to disrupt genetic equilibrium and cause evolution to occur?

1. Nonrandom mating 2. Small population size 3. Immigration or Emigration 4. Mutations 5. Natural Selection

What types of isolation lead to the formation of a new species?

1. Reproductive isolation 2. Behavioral isolation 3. Geographic isolation 4. Temporal isolation

What is the Bottleneck Effect?

A change in allele frequency following a dramatic reduction in the size of a population. It can sharply reduce a population's genetic diversity.

What is temporal isolation?

A form of reproductive isolation in which two or more species reproduces at different times.

What is evolutionary adaptation?

Any genetically controlled trait that increases an individual's ability to pass along its alleles.

What are the effects of small population size?

Because of genetic drift affecting populations strongly, evolutionary change happens more frequently.

Gene Pool

Consists of all genes, that are present in a population.

How is evolution defined in genetic terms?

Evolution involves a change in the frequency of alleles in a population over time.

Natural selection acts directly on....

phenotypes (not genotypes), therefore its characteristics (not directly the alleles)