Transcript Chapter 23 Notes: Population Genetics

DEFINITIONS
• POPULATION: a localized group of
individuals belonging to the same species
• SPECIES: a group of populations whose
individuals have the potential to interbreed
and produce fertile offspring (viable)
• GENE POOL: all alleles at all gene loci in
all individuals in a population
We all belong to
the same gene
pool!!!
A population of flamingos
6 different species of flamingo
DEFINITIONS
• Microevolution = studies how
pop’s of organisms change
from generation to generation
and how new species originate
• Macroevolution = studies
changes in groups of related
species over long periods of
geologic time; determines
evolutionary relationships
among species
Causes of Microevolution:
1) Natural Selection
2) Genetic Drift reduces genetic
diversity (changes in the gene
pool of a small population due to
chance)
Examples:
-Bottleneck Effect: results
from drastic decrease in
population size
-Founder Effect: few
individuals in a population
colonize a new habitat
Bottleneck Effect
3) Gene Flow (migration of fertile individuals
between populations)
4) Mutation (introduces new alleles into a
population)
5) Nonrandom Mating (individuals choose
mates based upon their traits)
Ways Natural Selection
Acts on a Population:
1) Stabilizing Selection: eliminates individuals
with extreme or unusual traits; existing
population frequencies of common traits are
maintained
*Example of Stabilizing
Selection in humans:
*human babies most commonly weigh 3-4 kg;
babies much smaller or larger have higher
infant mortality rates.
2) Directional Selection:
favors traits at one extreme of
a range of traits; common
during periods of
environmental change
Examples:
-insecticide resistance
-peppered moth
(Industrial Melanism)
Peppered Moth (Industrial
Melanism) example:
• 100 years after the first dark
moth was discovered in
1848, 90% of moths were
dark;
• the light variety continued to
dominate in unpolluted areas
outside of London.
3) Diversifying (a.k.a.
Disruptive) Selection:
occurs when environment
favors extreme or unusual
traits while selecting
against common traits
4) Sexual Selection: differential mating of males
in a population; leads to sexual dimorphisms
-females tend to increase their fitness by
increasing the quality of their offspring by
choosing superior male mates (and are therefore
“choosier” or more selective when finding a
mate)
Sexual Selection (cont.)
-males increase their fitness by maximizing the
quantity of offspring produced
**as a result, in vertebrate species,
the male is typically the
“showier” sex
-colorful plumage
-lion’s mane
-antlers