Ch. 17 Evolution Flashcards
Do organisms evolve
NO. Populations do
Population
An localized group if individuals that belong to the same species
Microevolution
Evolution within a population
Change of allele frequencies within a population
Gene pool
The total selection of genes (not individuals) in a population
Hardy Weinberg theorem
Describes a non evolving population
The frequencies of alleles and genotypes in populations will remain constant until acted upon aka Hardy Weinberg equilibrium
Genetic equilibrium
When the gene frequencies stay the same forever
Hardy Weinberg equation
p^2+2(pq)+q^2=1
Causes of micro evolution (what affects the allele frequencies)
If these are present…
Genetic drift Natural selection Gene flow Mutation Non random mating - if these are present then the population is not at genetic equilibrium
To be at hardy Weinberg equilibrium populations must…
Be large No migrations No mutations Random mating No natural selection
Genetic drift
-types
Small populations make it easier for the frequencies to “drift”. With only a few organisms it is more likely for one to be completely left out
- bottleneck
- founders effect
Bottleneck effect
The number of organisms in a population is drastically reduced. So only the alleles of the organisms who are left survive, this means some can be completely left out.
Founders affect
When some organisms settle a new area then only their genes are passed on to the population of that area, if they do not represent the gene pool of the larger source population then the frequencies here will be different and maybe more limited.
How do migrations effect a population?
If organisms are moving in and out then the allele frequencies will change.
Behavioral adaptions
Adaptions that effect the behavior of organisms
Causes them to behave a certain way…
Ex. Schools of fish
Penguins sitting on their eggs
Types/ effects of natural selection
Stabilizing
Directional
Disruptive
Sexual
Stabilizing selection
Individuals with average trait are more fit and extremes are not so curve gets skinnier
Ex. Plant height
Birth weight
Directional selection
One extreme is good the other is bad so the graph moves (toward the good trait)
Ex. Peppered moths
Disruptive selection
Both extremes are at an advantage but the average trait does well
Graph rises at both ends and sinks in the middle ^-^
Sexual selection
Males and females exhibit different traits
Ex. Male peacocks need to be bright to attract a mate
BUT females must be drab so they do not draw predators to their kids
Species
A population or group of populations whose members have the potential to interbreed with each other in nature to produce viable, fertile offspring
Prezygotic barrier
Barriers that prevent a zygote from forming
Either prevent mating or prevent fertilization
Post zygotes barriers
Barriers that prevent a zygote form growing and reproducing
Macro evolution
Evolution of one species into two or creation of a new species
Types of Prezygotic barriers
Temporal isolation Habitat Behavioral isolation Mechanical isolation Gamete isolation
