Download Evolution of Populations

BIOLOGY 12
Evolution
- Evolution of Populations
- Disruptions to Equilibrium
- Coevolution
- Pace
- New Species
Evolution of Populations
- Mechanisms
 population – localized groups of individuals
belonging to the same species
 gene pool – all of the genes present in a
species population
 gene (allele) frequency – proportion of each
gene (allele) in the gene pool
 genetic equilibrium – stability of the frequency
of genes in successive generations of a
population
Evolution of Populations…
 natural selection has an effect only on the
phenotype of an organism
 therefore heterozygote genotypes preserve
recessive genes in populations and variety is
conserved
 *if frequencies change, equilibrium is
broken and evolution occurs*
Disruptions to equilibrium are caused
by:
 1) mutations
 2) genetic drift – changes in the gene pool of
a population due to chance
two types:
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A) bottleneck effect – genetic drift that results
from a sudden decrease in population due to
environmental factors (fire, flood etc.)
B) founder effect – genetic drift that results from
a small population colonizing a new area
Bottleneck Effect
Example of a Bottleneck
 Northern Elephant
Seals
 population reduced
to as few as 20
individuals (due to
hunting)
 population has now
recovered to over
30 000 but little
genetic variation
Disruptions to equilibrium
continued…
 3) gene flow (migration) – the loss or gain of
alleles from a population due to the migration
of fertile individuals or the transfer of gametes
between a population
Coevolution
 when two or more species influence each
others evolution
 examples:
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flowering plants and their pollinators
predator prey relationships (newts)
leaf cutter ants and fungi
humans and symbiotic bacteria
humans and pathogenic bacteria (resistant
TB)
Pace of Evolution
two theories:
1) gradualism: states that populations slowly diverge
from one another by the accumulation of adaptive
characteristics within a population
*if this theory is correct, we would expect to find
many intermediate forms of species within the fossil
record; scientists have found intermediate forms of
only a few species, but some argue this is due to an
incomplete fossil record
Pace of Evolution continued…
2) punctuated equilibrium: evolution proceeds
with periods of inactivity (with little or no change)
followed by very active phases, so that major
adaptations or clusters of adaptations appear
suddenly in the fossil record
*this is supported by species who have not evolved in
millions of years and others that have changed a lot
within the last ~50 000 years
How do new species arise?
Divergent evolution: evolution in which
related species progressively differentiate
a major type of divergent evolution is
Adaptive radiation: the emergence of
numerous species from a common ancestor
introduced to an environment presenting a
diversity of new opportunities and problems
Textbook Questions
 1 – page 518
 1 – page 528
 7 – page 533
 10 and 16 – page 540
 1,3,4 and 5 – page 555
 4 – page 605