SPECIES-

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 factors:• Amount and quality of food

2) Heredity: (3 impacts) • 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 PrincipleWeinberg: 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 occur2. Individuals neither enter nor leave

through migration3. The population is large (ideally

infinitely large)4. Individuals mate randomly5. 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.

EX: Deep canyon or body of water separating the populations

2. Reproductive Isolation-• Inability of former interbreeding

organism to produce offspringPrezygotic 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

Patterns of EvolutionCoevolution:• The change of 2 or more

species in close association with each other

• EX: Predator/prey• The interaction between bats

and flowering plants (fur on bats face and flowers that are light colored)

Convergent Evolution• Organisms that are not closely

related become more similar.• Environment selects similar

phenotypes• EX: Sharks and Porposes

Divergent Evolution• 2 or more related species

become more and more dissimilar.

• Response to differing habitats

Adaptive Radiation: • Related species came from a

common ancestor (Darwin’s finches)

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 foreverCauses:• environmental