Download Evolution notes 2

Evolution – change in gene frequency
in a population over time (through
natural selection)
Natural selection
Variation
among
offspring
Too many offspring
CHANGES IN
Competition
ENVIRONMENT for resources
different rates of
survival and reproduction
Pepper moths
Light trees – light moths most common
After industrial revolution
Dark trees – dark moths most common
1990’s factories shut down
Light trees – return to light moths common
Species – type of organism that can only mate
with similar organisms to make viable fertile
offspring (AP book 474-5)
- Prezygotic barrier
Geographic isolation
Temporal (time) isolation
Behavioral isolation
-Postzygotic barrier
Reduced hybrid viability
Fertility
Breakdown
Sympatric speciation (shared space)
In same place – behavioral isolation
Temporal isolation
(season, time of day)
Allopatric speciation
Geographic speciation – separated by
physical barrier
Small populations
Genetic drift – gene frequency changes faster
by random chance
Examples:
Founder effect – small #s’ found a new
population
Bottleneck effect – decrease in genes due to
natural disaster
Cladogram – branching diagram showing
evolutionary relationships, where more close
together = more recent
Molecular clock – unique mutations occur at
fixed intervals (time), therefore can be used to
calculate rate of evolution