SpeciationEcology Unit

Speciation Formation of a

new species Species: A group of

similar organisms that breed together and produce fertile offspring.

Gene pools must become separated for them to become different species.

http://video.pbs.org/video/1300397304/

Speciation

Phenotype Observable

characteristics (green eyes,

brown hair, purple flowers, etc.)

Genotype Genetic makeup

of an organism determined by a pair of alleles.

All in the Genes

commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG

The genetic make-up of an organism is known as its genotype.

An organism’s genotype and the environment in which it lives determines its total characteristic traits.

its phenotype.PhenotypeGenotype

DNA

Watson and Crick and their model of DNA

www.chem.ucsb.edu/~kalju/chem110L/public/tutorial/images/WatsonCrick.jpgen.wikipedia.org/wiki/DNA

DNA replication

The double-helix structure of DNA was discovered in 1953.

This showed how genetic information is transferred from one cell to another almost without error.

Gene Unit of hereditary

information Located on a

chromosome Contains DNA Genes are passed

from parent to offspring.

Gene Pool Consists of all

the genes that are present in a population.

Genetic Variation Mutations

Any change in a sequence in DNA.

Few mutations lead to increased fitness.

Most mutations are harmful.

Mutations lead to variations in a population.

Variation

majorityrights.com/index.php/weblog/comments/racial_variation_in_some_parts_of_the_skull_involved_in_chewing/

Variationsof a particular gene are known as alleles.

For example, the one of the genes for hair color comprises brown/blonde alleles.

Species with greater genetic variability are more likely to adapt to changing environments

Natural Selection

en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg

Mutant alleles spread through a population by sexual reproduction.

If an allele exerts a harmful effect, it will reduce the ability of the individual to reproduce and the allele will probably be removed from the population.

In contrast, mutants with favorable effects are preferentially passed on

Selection of dark gene

Natural Selection can affect the distribution of phenotypes in any of three ways: Stabilizing Selection

Individuals at the middle of the curve have the greatest fitness.

Disruptive Selection Individuals at either end

of the curve have greater fitness than those in the middle.

Directional Selection Individuals at one end of

the curve have a higher fitness than those in the middle or other end.

Causes of SPECIATION

TigonTigonResult of male tiger and female lion mating incaptivity. Offspring are infertile.

Separated both geographically and ecologically.

Liger

Result of male lion and female tiger mating in captivity. Offspring are infertile.

Fig. 23.6

Four species of leopard frogs: differ in their mating calls. Hybrids are inviable.

Geographic Isolation

These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.

Temporal Isolation