Evolution and Natural Selection

Evolution: is a change in the frequency of alleles in a population

Charles Darwin
Source:http://homepages.ucalgary.ca/~jefox/Darwin.htm

DARWIN'S THEORY OF NATURAL SELECTION  has these basic ideas:

1. Perpetual Change
2. Common Descent
3. Speciation
4. Gradualism 
5. Natural Selection 

Darwin has his on way of observation in the population 

Observation 1: Organisms have a high potential fertility 

Observation 2: Natural population size is normally constant 

Observation 3: Natural resources are limited 

   ---> Inference 1: There exists continuing struggle for existence among the members in the population

Observation 4: All organisms show variation 

Observation 5: Some variation is inheritable 

    ---> Inference 2: There is differential survival and reproduction among varying organisms in a population

    ---> Inference 3: Differential survival and reproduction generate a new adaptation and new species

HARDY-WEINBERG PRINCIPLE
Hardy-Weinberg equilibrium: Shuffling of genes that occurs during reproduction, cannot change the overall genetic makeup in a population

Hardy-Weinberg equation: 

p²+ 2pq+ q² =1 

p: Dominant alleles 

q: Recessive alleles 

Requirement for a population in Hardy-Weinberg equilibrium

1. Population size is very large
2. Gene pool is isolated, no gene immigration and emigration 
3. Mating is random
4. Mutation does not change the gene pool
5. All individuals are equal in reproductive success 

Example: 

Imagine a population of 500 blue-footed boobies has different foot webbing. W is a dominant allele for non-webbed foot and w is a recessive allele for webbed foot. According to the researchers, there are  320 homozygous dominant boobies, 160 heterozygous boobies, and 20 homozygous recessive boobies. What is the frequency of alleles in this population? Given total alleles in gene pool in 1000

Solution: 

Check:

p= 0.8W

q= 0.2w 

Based on the Hardy-Weinberg equation: 

p²+ 2pq+ q² =1 

(0.8)² + 2(0.8)(0.2)+ (0.2)²=1

Reproductive Barriers
Pre-Zygotic: 
Temporal Isolation
Behavioral Isolation
Geographically Isolation
Mechanically Isolation
Gametic Isolation  

Post-Zygotic 
Hybrid Breakdown
Hybrid Sterility 
Hybrid Inviability 

Important Terminology
Gene Flow: A gain or loss of alleles in a population
Genetic Drift: A change of gene pool in a small population due to chance
Bottleneck Effect: A genetic drift resulting from a reduction of population size 
Founder Effect: random change of a gene pool that occurs in a small colony of a population. 

Reproductive Fitness: Ability for organisms to survive and reproduce
Adaptive Radiation  Evolutionary diversification that produces numerous ecologically disparate lineages from a single ancestor

Source: Lectured by Professor Blake Barron 
           Article: The Gene pool of a nonevolving population remains constant over the generation