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ABIO: Evolution Notes
I Introduction
Evolution – The change in a population of a species over time. The changes are the
result of changes in the gene pool of a population of organisms.
Population – a group of individuals of the same species living and reproducing in a
specific geographical area
Species – organisms that can mate and produce fertile offspring
Gene pool – the sum total of all alleles in a population
1. Allele frequency – how often an allele occurs out of all the alleles
2. Phenotype frequency – - how often a phenotype occurs out of all the
phenotypes
II. Mechanisms of Evolution – Allele frequencies in a population can change
(and thus evolution can occur) as a result of:
1. Mutations – Mutations may
produce new alleles that result in a
new phenotype that offer an
advantage in a population. Mutations
also introduce genetic diversity
2. Gene Flow – the process of genes moving from one population to another
a. Emigration – movement of individuals out of a population
b. Immigration – movement of individuals into a population
3. Genetic Drift – allele frequencies in a population change as a result of random
events, or chance
a. Effects small populations more
b. Bottleneck Effect – a catastrophic event (earthquake, fire, etc) occurs
and only a few organisms survive, surviving organisms do not represent
the allele frequencies from the original population
c. Founder Effect – a few individuals that do not represent the overall allele
frequencies of the larger population leave to start a new population
4. Nonrandom Mating - mate selection may be influenced
by geographic proximity, selecting a mate with similar
traits, sexual selection (females choosing mates basic on
certain traits)
5. Natural Selection – survival and reproduction of
individuals based on inherited traits. Those organisms with
certain phenotypes may be better adapted to their
environment and will survive and reproduce. The frequency
of the alleles for that phenotype will increase in the
population.
III. Speciation – the process of species formation.
Occurs when the gene pool for a group of organisms becomes reproductively
isolated from the original population (which can occur by any of the mechanisms
listed above).
Isolating mechanisms – features or behaviors that prevent mating
or breeding between two different species. Can create or
maintain reproductive isolation.
1. Geographic Isolation – Population is separated by some
physical feature (mountains, river)
2. Temporal Isolation – individuals mate at different
times of day or year
3. Behavioral Isolation – individuals don’t recognize
mating behaviors of another species
IV Evidence of Evolution – many types of evidence support the theory of
evolution:
A. Fossils
1. In sedimentary rock
2. Imprints in soft
sediment that hardens
3. Petrification – replacement of bones by minerals
4. Amber – think Jurassic Park
B. Anatomical Evidence
1. Homologous Structures – structures are similar but with
different functions (share a common ancestor)
a. Example – arm of a person, wing of a bird
b.
2. Analogous Structures – structures are different but have
similar functions (evolved independently)
a. Example – wing of a bee, wing of a bird
3. Vestigial Structures – structures that no longer have a useful
function
a. Examples – 3rd eyelid, appendix, tailbone (in
humans), wisdom teeth
C. Embryological Evidence 1. Comparing the embryos and their development among different
animals
D. Biochemical/Molecular Evidence
1. All species use similar proteins/chemicals in their bodies
2. Examples –Structures and functions of molecules such as ATP,
insulin, DNA are similar in many living things
OVERALL CONCLUSION: ALL ORGANISMS ON EARTH HAVE DESCENDED
FROM A COMMON ANCESTOR