HOW DOES EVOLUTION WORK? By: A Good Student. What is Evolution? Evolution is descent with...
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Transcript of HOW DOES EVOLUTION WORK? By: A Good Student. What is Evolution? Evolution is descent with...
HOW DOES EVOLUTION WORK?
By: A Good Student
What is Evolution?
Evolution is descent with modification. On a small scale, this can be changes in
the gene frequency of a population over time.
On a large scale, this can be the descent of different species from a common ancestor
How Does Evolution Work?
Evolution depends on genetic variation and the resulting phenotypic variation in populations.
Sources of genetic variation Mutations Recombination Sex
Mechanisms of Evolution
Natural Selection Sexual Selection
Mutation Genetic Drift Gene Flow (Migration)
Natural Selection
Variation exists in populations Variation is heritable Variation influence reproductive success Helpful variations are passed on to the
next generation in greater abundance
Natural Selection: an example Variation in beak size in Galapagos
finches Beak size is a heritable trait After a drought, individuals with bigger
beaks survived better and reproduced more often
The next generation had a larger average beak size
Sexual Selection
A “special case” of natural selection Occurs because of nonrandom mating Acts on an individual’s ability to attract a
mate Example: Male guppies have bright spots to
attract females Can work in the opposite direction of
natural selection Example: Predators can see bright males
more easily
Mutation
A mutation could cause parents with genes for one trait to produce children for genes with another trait
Example: Marfan Syndrome
Spontaneous mutation causes a connective tissue disorder
This is passed on to offspring
Genetic Drift
Due to random factors or chance (not selective pressures), individuals with one genotype produce more offspring
Occurs in small population sizes Founder effect: a small group breaks off
from the large, limiting the gene pool Bottleneck effect: population size reduced,
genetic variation decreases
Genetic Drift: an example
Northern elephant seals were hunted by humans Decreased population size and genetic
variation Population size has rebounded Genetic variation has not
Display less variation than southern elephant seals that were hunted less
Gene Flow
When organisms from one population migrate to another population, they change the composition of the gene pool of both populations
Example: If all the red headed people left Scotland,
the next population would have less people with the trait. The place where they migrated to, would have more.
Speciation
Mutation, Natural Selection, and Genetic Drift would all act to increase the likelihood of speciation because they increase genetic diversity between the two populations.
Gene flow would reduce the likelihood of speciation because it makes populations more genetically similar.
Speciation
Speciation occurs when two or more species (group of interbreeding individuals) come from a single species. The general causes of speciation are genetic drift and gene flow. Allopatric speciation: occurs when a specific barrier
exists to isolate two populations geographically, preventing them from interbreeding Peripatric speciation: a type of allopatric speciation that
occurs when one of the isolated populations is very small Parapatric speciation: occurs when there is no specific
geographic barrier present; organisms are more likely to reproduce with individuals closer to them than further away in the geographic range of the species
Sympatric speciation: occurs when there is no geographic distance or barrier present; instead some individuals might start to exploit a new niche, creating a divide between the population
Sources
http://evoultion.berkeley.edu/evosite/Evo101.html
http://evolution.berkeley.edu/evosite/search/search_lessons.phpsort_by=audience_rank&topic_id=&keywords=teach+about+homologies&Submit=Search