THEORY OF EVOLUTION II

How Evolution Occurs Genetically

HOW EVOLUTION WORKS Evolution occurs in _populations_ not

_individuals.   Why? Within the _lifespan_ of one

individual, new features cannot evolve in

response to _natural_ selection. Only as

traits are inherited, can the _environment select for them

GENETIC EQUILIBRIUM _gene_ _pool_ is the entire collection of

genes in a population.

GENETIC EQUILIBRIUM If you know the genotypes of a population,

you can calculate the _allelic  _frequencies, or the percentage of an

allele in a population.   When the frequency of alleles is not

changing from generation to generation the  

population is in _genetic_ _equilibrium.

When allelic frequencies are changing, the population is evolving.

WHAT CAUSES GENETIC CHANGE Hardy-Weinberg postulated that

populations WILL NOT change allelic frequenices if these five conditions are met:

A. No Mutation B. Large population C. No migration D. Random mating E. No natural selection

WHAT CAUSES GENETIC CHANGE _Mutation___ is any change in DNA. While

most

often _harmful in some cases it can be _beneficial_.

  Causes: a. _chemicals____   b. _radiation___   c. _DNA replication errors__

WHAT CAUSES GENETIC CHANGE 2._genetic _drift is random change of allelic   frequencies due to _chance. More important in

_small_ _populations_ than large ones.   For example, there is village in Spain that is

polydactyl, that recessive gene shows up in a   much larger percentage_ than normal due to chance.

Continued inbreeding in the same population _concentrates_ the trait.

GENETIC DRIFT

WHAT CAUSES GENETIC CHANGE 3. _Migration___   Individuals _enter_ or _leave_ a

population

either adding or subtracting alleles from a population.

WHAT CAUSES GENETIC CHANGE 4. Sexual selection is non-randoming

mating, which can result in dramatic evolution of certain traits.

WHAT CAUSES GENETIC CHANGE 5. Natural selection will always cause

allelic change due to survival differences.

HOW NATURAL SELECTION ACTS ON POPULATIONS Variations tend to go over a _range.   Ex – Height of people.           Selection occurs when _one area__ of

traits are favored

NATURAL SELECTION 1. Stabilizing __selection__ is when

average individuals in a population are favored. This reduces __variation_ in a population

NATURAL SELECTION 2. directional _selection is when one extreme form of the trait is favored.

This can lead to rapid _evolution in a population.

NATURAL SELECTION 3. disruptive _selection_ is when

selection favors both the extreme forms of a variation. May lead to new _species_.

 

EVOLUTION OF SPECIES A _species are organisms that basically

look

similar and can have fertile offspring.   _speciation_ is the evolution of a new

species.

EVOLUTION OF SPECIES 1. geographic isolation is when a

physical

Barrier separates two groups leading to _unique gene pools. _Australia__

 is considered a good example of this

EVOLUTION OF SPECIES 2. _reproductive_ isolation is when

Formerly interbreeding organisms no longer produce viable offspring. Happens in two ways:

  _reproductive, genetic differences lead to

death of embryo.   seasonal, animals start breeding at

different times of the year based on their environment.

EVOLUTION OF SPECIES 3. polyploidy is when, during meiosis,

extra

chromosomes are added to the genome. This is seen in plants. Perhaps _half_ of

  all flowers_ and _crops_ are polyploid.

It

leads to new species instantly.

GRADUALISM V. PUNCTUATED EQUILIBRIUM 1. ._gradualism is the idea that species

develop through the slow buildup of

adaptations. This was _Darwin’s_ view.

However, many species have been amazingly stable over time.

GRADUALISM V. PUNCTUATED EQUILIBRIUM punctuated equilibrium says that

living

Things have long periods of stability with speciation that occurs in rapid bursts. This is

  caused by changes in the environment

or introduction of new alleles.

CONVERGENT V. DIVERGENT EVOLUTION . convergent evolution is when two

species

evolve similar adaptations in different locations. This happens with geographic isolation 

Ex. Rabbits and patagonian hares_

CONVERGENT V. DIVERGENT EVOLUTION 4. divergent evolution is when two

species grow less alike over time due to reproductive isolation.

Ex. African and Asian elephant