SPECIES-

• A group of individuals that look similar and whose members are capable of producing fertile offspring.

The definition of species derived from two different “concepts”…

1) Morphological Species Concept:

• Based on internal and external similarities and differences.

• MORPHOLOGY

2) Biological Species Concept;• Classification based on an organisms ability to reproduce and produce fertile offspring.

The offspring of two morphologically dissimilar organisms

HYBRID:

*POPULATION-

• All members of the same species that live in a particular area at the same time.

• Within a population, individuals vary in many observable traits

• These can be presented on a BELL CURVE.

What causes variations within species…

1) Environmental factors2) Heredity • mutations• genetic recombination• crossing over

Allele Frequency and Genetic Equilibrium

A population is a collection of genes

GENE POOL- • A collection of genes for all the

traits of a population.

ALLELE FREQUENCY- • The % of a specific allele

of a certain gene in the gene pool

GENETIC EQUILIBRIUM-• A population in which allele

frequency does not change.

The Hardy-Weinberg Principle

Weinberg: German physicianHardy: British mathematician

* Observed that allele frequencies in populations remain relatively the same unless acted on by outside influences

Assumptions for Equilibrium:

1. No mutations occur

2. Individuals neither enter nor leave through migration

3. The population is large (ideally infinitely large)

4. Individuals mate randomly

5. Natural selection doesn’t occur

p2 + 2pq + q2 = 1.0 DEMO PROBLEMS:

Disruption of Genetic Equilibrium

A. Mutations-• Physical change of genes or

chromosomes• Produce totally new alleles for

a trait• Can change the frequency of

alleles

B. Migration-

immigration:• movement into a populationemigration: • movement out of a population*Gene flow- The movement of genes into or

out of a population through migration.

C. Genetic Drift-

• Allele frequency in a population changes as result of a random event

Genetic Drift-• Significant only in small and

medium sized populations• An allele may disappear

completely in a small population• More stable in larger

populations

D. Non-Random Mating• Random mating is a requirement

for genetic equilibrium• Many species DO NOT follow

random mating.• Mating is influenced by a variety of

factors…

Reasons for Non-Random Mating:

• Geographic proximity• Selection based on similar physical

characteristics• ASSORTIVE MATING

PROBLEMS FROM NON-RANDOM MATING:

• Mating may amplify certain recessive disorders.

“Survival of the fittest”

• Some members of a population are more likely to contribute genes

E. Natural Selection-

Types of Natural Selection

1. Stabilizing Selection-

• Natural selection in which individuals with the average form of a trait have the advantage.

• Natural selection in which individuals with one of the extreme forms of a trait has an advantage.

2. Directional Selection

3. Disruptive Selection• Type of natural

selection in which individuals with either of extreme forms of a trait have advantage.

4. Sexual Selection-

• Mate selection based on the presence of a specific trait.

• The formation of a new species

Speciation-

Isolated Populations…

1. Geographic Isolation-• A physical separation of

members of a population.

2. Reproductive Isolation-• Inability of former interbreeding

organism to produce offspring

Prezygotic Isolation:• Obstacle occurs before fertilizationExamples:• Incompatible behavior

• Different mating calls• Different mating seasons

Postzygotic Isolation:• Obstacle occurs after fertilization

Examples:• Offspring may not develop

completely• Offspring may die early• Offspring may not be fertile

RATES OF SPECIATION2 major theories regarding the rate of

speciation:Gradualism:• The idea that divergence of species

occurs smoothly and gradually over time

PUNCTUATED EQUALIBRIUM-

The idea that things live in Genetic Equilibrium then changed in short spurts of time.

• Unicellular organisms may evolve in months or even day

• Other evidence suggests within thousands of years

EXTINCTION:• The point at which

no organisms of a particular species are available to reproduce

• change• Disruption of

habitat

• Natural process, ongoing• Once gone, gone forever• Causes:• environmental