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LESSON 2 – MECHANISMS OF EVOLUTION
• Evolution – change in allele frequencies over
time.
• Natural selection – the process by which
certain individuals are more likely to survive
and reproduce, leading to changes in the
alleles of a population or species.
• Alleles for traits that give an advantage in
survival and reproduction are more likely to be
passed on to offspring.
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Classic Example
Peppered moths in the United Kingdom
They were grey with black speckles in 1800s
This helped to camouflage the moths against the
lichen-covered trees of the moth’s environment,
helping to avoid predators.
• The Industrial Revolution – coal burning released
soot that settles on trees
• Then black-colored peppered moth were
observed.
• Moths that were black were more likely to
survive then reproduce then more in the
population increased.
• ALLELE FREQUENCY
• How common an allele occurs in a population.
An allele with a higher frequency is more
common than one with a lower frequency.
• NATURAL SELECTION PRINCIPLES:
1. Organisms produce more offspring than their
environments can support.
2. Offspring vary in phenotype.
3. Variation is caused by differences in alleles
inherited.
4. The inheritance of alleles determines how
likely an individual organism is to survive and
reproduce.
5. Only “helpful” alleles will be passed on to
future offspring.
• MECHANISMS OF EVOLUTION
• Population – group of organisms of the same
species that share a geographical area and
breed with each other.
• Genetic drift – changes in allele frequencies
that are due to chance events.
– Migration – movement of individuals into or out
of a population.
– Founder effect – formation of a new population
from just a few individuals who leave a larger
population.
– Population bottleneck – when an entire
population is reduced to just a few individuals,
often as a result of some form of disaster such as
disease.
• Speciation – formation of new, genetically
distinct species from populations of existing
species.
• Geographical isolation – divides two
populations through a physical barrier, such as
a canyon, river, or highway.
• Reproductive isolation – prevents this
population from mating with members of the
original population.
• Species – a group of organisms that can mate
and produce fertile offspring.
• Isolating mechanisms – physical or behavioral
trait that prevents a member of one species
from mating with a member of a different
species and producing fertile offspring.
• https://www.youtube.com/watch?v=aTftyFbo
C_M&list=PLT_3xjjmTinZcgruya5D1B5XLrB3sR
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