EVOLUTION OF POPULATIONS

What is evolution? The change in the genetic make-up of a species over timeThe change in the genetic make-up of a species over time

POPULATION GENETICS What is a population? What is a population? A collection of individuals of the same species living in the same location that routinely interbreed.A collection of individuals of the same species living in the same location that routinely interbreed. A species is a naturally breeding group of organisms that produce fertile offspring. A species is a naturally breeding group of organisms that produce fertile offspring. A population is the smallest unit in which evolution occurs A population is the smallest unit in which evolution occurs

What is a “gene pool”? Gene pool – total genetic information available in a population (ie., all the genes in a mating population) Gene pool – total genetic information available in a population (ie., all the genes in a mating population)

Allele Frequency How often is one particular allele seen in an individual How often is one particular allele seen in an individual Total of all allele frequencies = 100% or 1 Total of all allele frequencies = 100% or 1 p = frequency of one allele p = frequency of one allele q = frequency of the other allele q = frequency of the other allele So, what does p + q = ______? So, what does p + q = ______?

Individuals within a population vary. Biologist study the variation. A bell curve represents the distribution of variants in a population.

What causes variation? Recombination * Crossing-over * Independent assortment of alleles * Independent assortment of alleles Mutations Random fusion of gametes fertilization fertilization

Hardy-Weinberg Equilibrium The allele frequency in a population can be calculated using the Hardy-Weinberg equation. The allele frequency in a population can be calculated using the Hardy-Weinberg equation. This equation states that all of the allele combination must add to ONE (1) This equation states that all of the allele combination must add to ONE (1) Dominate alleles + recessive alleles = 1 Dominate alleles + recessive alleles = 1 p + q = 1 p + q = 1 The frequency of the heterozygote may also be calcuated The frequency of the heterozygote may also be calcuated

Allele frequency tends to remain the same from generation to generation unless acted upon by an outside force.

What is Hardy-Weinberg Equilibrium? Assumes NO evolution occurs. Assumes NO evolution occurs. All 5 conditions must be meet. All 5 conditions must be meet. Can never happen! Can never happen! It is a model or a yardstick to measure how much a population or species has evolved. It is a model or a yardstick to measure how much a population or species has evolved.

Hardy-Weinberg Equilibrium Conditions No net mutation No net mutation No migration No migration Large population size Large population size Mating is random Mating is random Natural selection does not occur Natural selection does not occur

Disruption of Genetic Equilibrium Mutation Mutation Migration Migration Migration Genetic Drift Genetic Drift Genetic Drift Genetic Drift Non- Random Mating Non- Random Mating Non- Random Mating Non- Random Mating Natural Selection Natural Selection Natural Selection Natural Selection

MIGRATION Immigration Immigration Emigration Emigration Gene flow – moving genes from population to another Gene flow – moving genes from population to another

Genetic Drift Change in the allele frequency as a result of random events or chance Change in the allele frequency as a result of random events or chance Usually occurs in small populationsUsually occurs in small populations After a natural disastersAfter a natural disasters Flood Flood Forest fire Forest fire In the smallest population allele frequency reaches 0 after the 45 th generation = no variation

Non-random Mating Random Mating – mating without regard to genetic make-up Random Mating – mating without regard to genetic make-up Sometimes mating selection is often influenced by geographic proximity Sometimes mating selection is often influenced by geographic proximity Many animals do not mate randomly Many animals do not mate randomly

NATURAL SELECTION 1 All species have genetic variation. 2. The environment presents many challenges 3 Organisms tend to produce more offspring than the environment can support - competition ( struggle for survival) 4 Some individuals are better suited to cope with the challenges ( survival of fittest) 5 Characteristics best suited to environment tend to increase in a population over time

Sexual Selection

STABILIZING SELECTION Individuals with the average form are of a trait have the highest fitness Individuals with the average form are of a trait have the highest fitness Example: 1. Birth weight in offspring 2. Seed size

DIRECTIONAL SELECTION The frequency of one allele tends to move in one direction ( more of one of the extremes forms of the trait The frequency of one allele tends to move in one direction ( more of one of the extremes forms of the trait Example – tongue length in anteaters

Disruptive Selection Individuals with either extreme have an advantage over individuals with the average form of the trait. Example: Limpet shell coloration

Types of Isolation Geographic isolation – impenetrable barrier separates Geographic isolation – impenetrable barrier separates Temporal isolation – breeding seasons are at different times Temporal isolation – breeding seasons are at different times Behavioral isolation – mating behavior does not attract female Behavioral isolation – mating behavior does not attract female

SPECIATION Development Development of a new species from an existing one (due to competition, geographic isolation) Results Results in reproductive isolation It is advantageous for the finches to develop different food sources (thus different shaped beaks) to reduce competition.

How does evolution/speciation occur? GRADUALISM gradual process that goes on all the time PUNCTUATED EQUILIBRIUM periods of rapid change are separated by periods of little or no change

MICROEVOLUTION LEADS TO MACROEVOLUTION (individuals don’t evolve … populations do)