Download Evolution

Evolution
Natural Selection
Microevolution
Macroevolution
Is evolution really taking place?
Hardy – Weinberg Equilibrium
1. Large population
2. Random mating
3. No mutations
4. No migration
5. No natural selection
If these conditions are true than there is NO Evolution.
NO change in gene frequency from generation to generation.
To prove this they developed the:
Hardy-Weinberg Equation
p+q=1
p2 + 2pq + q2 = 1
Where p = Dominant Allele and q = Recessive Allele
By knowing the number of Dominant and Recessive alleles of a gene in
the population you can predict the phenotype of the members of the
population and visa versa. If the conditions of the Hardy-Weinberg
Equilibrium are maintained then the population should remain constant
generation after generation.
Natural selection
The natural process that results in the adaptation of a population to
the living and nonliving factor in a region.
Darwin believed this was the mechanism for all of evolution.
Steps of natural selection:
Over production
Competition
Variation
Adaption
Speciation
Darwin didn’t understand the genetic component behind this process.
Microevolution
• Evolution that occurs on the population
and species level
• Caused by:
»
»
»
»
»
Gene Mutations
Genetic Drift
Founder Effect
Bottleneck Effect
Non-random Mating
Microevolution
Gene mutation
• Directional Selection
• Stabilizing Selection
• Disruptive Selection
What defines a species?
Two organisms that can reproduce in nature and produce offspring that
are fertile and can reproduce are the same species.
Gene Mutation
A sudden change in the genetic sequence of an organism
Point mutation: Where a single nitrogenous base in a gene is
altered effecting one amino acid the protein.
Example: sickle cell anemia is only one base different than
normal hemoglobin
Frames Shift mutation: Deletion of a base which causes a
change in the overall sequence of amino acids in a protein
Genetic Drift
New population is started with just a few members of original population so the gene pool
is limited. The only variations that show up in future generations are those found on
those limited number of genes.
Original Population
Migration
New Population
Offspring
Genetic Drift - Bottleneck Effect
A barrier, over hunting or habitat loss prevents the interaction of a new populations with
the original population limiting genetic diversity.
MacroEvolution
• Evolution that occurs on the community
level effecting many different species.
•
•
•
•
Prezygotic – Before a zygote forms
Postzygotic – After the zygote forms
Allopatric Speciation – “ Other Country”
Sympatric Speciation – “ Same Country”
Prezygotic – Factors that prevent an organism from mating and
having offspring.
These can include habitat isolation, temporal isolation, mechanical
isolation and behavioral isolation
Postzygotic – Mating takes place and a zygote is formed but it
doesn’t produce any new offspring.
This can include zygote mortality, hybrid sterility
Allopatric - Part of a population is separated from the original
population and geographically isolated from it leading to reproductive
isolation. Variations occur due to genetic drift and mutations with
each population
Synpatric – Groups within a population become reproductively
isolation from each other. This can be the result of mating behaviors,
habitat and food preferences. Changes occur due to genetic drift and
natural selection.
Adaptive Radiation
When new organisms comes into to a region where there are many
unoccupied niche the organisms will spread out and find a niche that
offers the least competition with its neighbors. Over time the
population will adapt to that niche and only interact with similar
members of the population occupying that niche.