Transcript Mechanisms of Evolution

Mechanisms of Evolution
Hardy-Weinberg Principle
A. A population is in genetic equilibrium—all
individuals are equally adapted to their
environment & contribute equally to the next
generation
1. Five conditions for this to occur
a. No Genetic Drift
b. No Gene Flow
c. No Mutations
d. Mating must be random
e. No Natural Selection
Genetic Drift
B. Chance occurrences can cause an allele to become more
or less common
Founder Effect: result of migration (Darwin’s finches)
Ex. Amish and Mennonites: people rarely marry outside their own
communities; Old Order Amish—high frequency of 6-finger
dwarfism—can trace ancestry back to one of the founders of the
order
2. Bottleneck: result of a dramatic reduction in population size and then
rebounds; might be a possible factor in the potential extinction of a
species
Ex. Cheetahs in Africa are so genetically similar they appear inbred;
researchers think there was a bottleneck 10,000 yrs ago, and then
again 100 yrs ago
1.
Gene Flow
C. Rate at which genes enter or leave the population—
random migration naturally increases variation
Nonrandom Mating
D. Organisms usually mate w/individuals in close
proximity which promotes inbreeding
Mutation
E. Some are harmful, some are advantageous
Natural Selection
F. Acts to select those individuals that are best
adapted for a particular environment
Reproductive Isolation
G. Prevents gene flow among populations
Ex. 2 species can mate to produce a hybrid
which is sterile (liger)
**Other forms of isolation are more specific forms
of this
Speciation
H. Population diverges and new species is
reproductively isolated
Patterns of Evolution
A. Adaptive Radiation: many related species evolve
from a single species (Darwin’s finches)—usually
due to different environments Ex. guppies in a
pool on the same river
B. Coevolution: 2 or more species change together
C. Convergent Evolution: 2 unrelated species have
similar characteristics
D. Rate of Speciation: usually is gradual, but there
have been periods of abrupt transitions
Adaptive Radiation
Coevolution
Acacia ants live in thorns of
acacia tree. Plant make
substance used by ants as food.
Ants defend tree from herbivores
by attacking/stinging any animal
that brushes up against the tree
Convergent Evolution
Rate of Speciation