EVOLUTION & SPECIATION

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Microevolution. What is it?

• changes in the gene pool of a population over time which result in relatively small changes to the organisms in the population

• changes which would not result in the newer organisms being considered a different species.

• Examples would include a change in a species’ coloring or size.

VOCABULARY REVIEW• EVOLUTION – CHANGE OVER TIME

• NATURAL SELECTION INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE– A.K.A. “SURVIVAL OF THE FITTEST”

NEW VOCABULARY

• POPULATION GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED

• GENE POOL COMMON GROUP OF ALL GENES PRESENT IN A POPULATION

Evolution of Populations

Occurs when there is a change in relative frequency of alleles

Gene PoolCombined genetic

information of all members

Allele frequency is # of times alleles occur

For some traits certain phenotypes appear more frequently

Variation in Populations2 processes

can lead to this:

Mutations -change in DNA sequence DO not always

change the phenotypes, but can affect an organisms 'fitness'.

Gene Shuffling –

from sexual reproduction

Mechanisms of Microevolution

1.Natural Selection2.Sexual Selection3.Genetic Drift4.Gene Flow

• Natural Selection: environment increases the frequency of alleles that provide a reproductive advantage

• only form of microevolution that adapts a population to its environment

Generation 1: 1.00 not resistant0.00 resistant

Resistance to antibacterial soap

How natural selection works

Resistance to antibacterial soapGeneration 1: 1.00 not resistant

0.00 resistant

mutation!

Resistance to antibacterial soapGeneration 1: 1.00 not resistant

0.00 resistant

Natural Selection on Different Traits

3 Types that affect the phenotypes in a population

1. Shifts to middle range

2. Shifts to 2 extremes

3. Shifts to 1 extreme

1. Stabilizing Selection- individuals near the center of the phenotype range have a higher fitness then those at both ends.

2. Directional Selection- Population may find itself in circumstances where individuals occupying one extreme in the range of phenotypes are favoured over others

3. Disruptive Selection- occurs when both extremes are favoured in a population.

Sexual selection• Sexual

dimorphism: secondary sex characteristic distinction

• Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism

• Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different genotypes)

•Genetic Drift = changes to allele frequency as a result of chance

Genetic Drift changes populations…….• Example- Random change in

allele frequency causes an allele to become common

• Bottleneck effect = dramatic reduction in population size usually resulting in significant genetic drift• Occurs when disasters such as earthquakes, floods, droughts, and fires reduce the population

• Founder Effect: - Genetic Drift that occurs when individuals from a large population leave to establish a new population

- Allele frequencies of the new population will not be the same as those of the original

• Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

SPECIATION• THE FORMATION OF NEW

SPECIES

• AS NEW SPECIES EVOLVE, POPULATIONS BECOME REPRODUCTIVELY ISOLATED

• REPRODUCTIVE ISOLATION – MEMEBERS OF 2 POPULATIONS CANNOT INTERBREED & PRODUCE FERTILE OFFSPRING.

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

SPECIATION IN DARWIN’S

FINCHES• SPECIATION IN THE GALAPAGOS

FINCHES OCCURRED BY:

- FOUNDING OF A NEW POPULATION,

- GEOGRAPHIC ISOLATION which led to -- REPRODUCTIVE ISOLATION and

CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.

Evidence of Evolution1. Fossil Record

2. Geographic Distribution of Living Species

3. Homologous Body structures

4. Similarities in Embryology

Evidence of Evolution

Fossil Record provides evidence that living things have evolved

Fossils show the history of life on earth and how different groups of organisms have changed over time

EVOLUTION & SPECIATION

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