Transcript Population Evolution

Population Genetics
The study of allele
frequencies within a
population
Gene Pool
• All of the genes of a population of
organisms
– Organisms that are the most
successful at reproducing contribute
most to the gene pool
Evolution
• Any change in the frequency of
any allele within a gene pool
– Populations undergo evolution
– Individuals do not undergo
evolution
Factors Affecting the Allele
Frequency
• Mutation
– Especially important for
organisms with short generation
times
Factors Affecting the Allele
Frequency
• Migration
– Movement of organisms into or
out of the population
Factors Affecting the Allele
Frequency
• Genetic Drift
– Random change in allele
frequencies
– Occurs mostly in small, isolated
populations
Factors Affecting the Allele
Frequency
• Selection
– Environmental pressures
– Competition
– Climate change
Factors Affecting the Allele
Frequency
• Nonrandom mating
– Preferences in selection of a
mating partner
SPECIES
Species: A group
of organisms so
similar to one
another that they
can interbreed and
produce fertile
offspring
Kingdom
Phylum
Class
Order
Family
Genus
Species
Speciation
• Speciation is the evolution of
new species through time
• Speciation occurs most rapidly
in a small population
Mechanisms of Speciation
• Artificial Speciation
– New species have been developed
by man
Intentional mutations
• Cross breeding
• Genetic engineering
•
Mechanisms of Speciation
• Natural Speciation by Isolation of
Small Populations
– Geographical Isolation
• Geographical barriers separate two
populations
– Mountain ranges
– Deep canyons
– Bodies of water
– Ecological Isolation
• Organisms of two populations require
different habitats
Mechanisms of Speciation
• Behavioral Isolation
– Changes in habits that identify one
population with another
• Mating rituals
• Methods of communication
Mechanisms of Speciation
• Seasonal Isolation
– Reproductive cycles do not
coincide
• Plants that flower at different
times
• Animals that mate or nest build at
different times
Mechanisms of Speciation
• Mechanical Isolation
– Physical characteristics that keep
organisms from interbreeding
• Difference in size
• Difference in reproductive anatomy
• Inability of sperm to penetrate the
egg
Observations From the Fossil
Record
• Species often remain stable for
millions of years with little or no
noticeable change
• Species may disappear rapidly and
new species may appear just as fast
Population Evolution
Punctuated
Equilibrium
Long periods of
stability followed
by short periods
of rapid change