17.2: Evolution as Genetic Change in...
Transcript of 17.2: Evolution as Genetic Change in...
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