17.2: Evolution as Genetic Change in Populations

Evolutionary Fitness: success in passing genes to gen

Evolutionary Adaptation: genetically controlled trait indiv’s ability to pass its alleles

1. Natural Selection on Single-Gene Traits:

Changes in allele freq. changes in phenotype

Causes Genetic Change

2. Natural Selection On Polygenic Traits

More complex

Can affect fitness of phenotypes to prod 1 of 3 types of selection

Directional

Stabilizing

Disruptive

Indiv at 1 end has fitness than indiv at middle or end

Range of phenotypes shift b/c more successful at surviving & reprod

Indiv near center of curve have fitness than indiv at either end

Keeps center of curve at current position

Narrows curve overall

Indiv at outer ends of curve fitness than indiv near middle

Acts against indiv of intermediate type

Can use split of curve into 2

A change in gene pool (allele freq) due to chance

1. Genetic Bottlenecks:

Reduction due to natural disasters & hunting

Reduce the size of pop

2. The Founder Effect

Few indiv colonize an isolated island, lake, or new habitat

Smaller colony, less its genetic makeup will represent original colony

Change reduces genetic variation

Genetic Equilibrium: allele freq in pop remain the same

Hardy-Weinberg Principle: allele freq in pop remain constant unless 1 or more factors cause freq to change

5 conditions that cause evolution to occur:

1. Nonrandom Mating

2. Small Pop size

3. Immigration or Emigration

4. Mutations

5. Natural Selection

Species: pop or grp of pop that can interbreed & produce fertile offspring

Speciation: formation of new species

Interbreeding genetically links members

Reproductive Isolation: 2 pop no longer interbreed, split gene pool; evolve into 2 sep species

Behavioral Isolation

Geographic Isolation

Temporal Isolation

2 pop develop differences in courtship rituals or other behaviors that prevent them from breeding.

2 pop separated by geographic barriers ex: rivers, mountains, water

2 or more species reproduce at diff times can not interbreed

Ex: flowers bloom at diff times, can’t pollinate one another