Download The Evolution of Populations

The Evolution of
Populations
Overview the smallest unit of
evolution
True or False:
– Organisms evolve, in the Darwinian sense, during
their lifetimes
– Individuals evolve
– Populations evolve
– Genetic variations in populations contribute to
evolution
Gene Pools and Allele Frequencies
Population- a localized group of individuals that are
capable of interbreeding and producing fertile
offspring.
Gene pool- the aggregate of genes in a population at
any one time
Thus a species may have two populations… ex. Caribou
populations in the Yukon
• Fixed allele- all individuals are homozygous, only one
allele exists in the population for that gene
Concept 23.1: Population genetics provides a foundation
for studying evolution
Microevolution- change in the genetic makeup of a
population from generation to generation
Different from Darwin’s definition of evolution
• Darwin explanation of evolution considered
unsatisfactory because did not consider how the
heritable variations required for natural selection
appear in populations or how organisms transmit
these variations to their offspring
The Modern Synthesis
Population genetics- the study of how populations
change genetically over time
Modern synthesis- a comprehensive theory of
evolution that integrated ideas from many other
fields.
Mendelian genetics
Darwinian theory of evolution through natural selection
Hardy- Weinberg
Theorem
This theorem states that the frequencies of alleles and
genotypes in a population’s gene pool remain constant
from generation to generation , provided that only
Mendelian segregation and recombination of alleles are at
work.
Involves gene pools that are not evolving
Mendelian inheritance preserves genetic variation from
one generation to the next
Hardy-Weinberg equilibrium describes a population in
which random mating occurs
It describes a population where allele frequencies do not
change
(p+q)
X
Allele frequencies
Of male gametes
(p+q)
=
allele
(p2+2pq+q2)
genotype
frequencies
frequencies
of female
in next
generation
gametes
Proportionally at a locus with with two alleles, the
three genotypes will equal one:
p2+2pq+q2=1
Meaning a population which continued to mate
randomly generation after generation, would have
allele and genotype frequencies which remained
constant
For a Population to be
in Hardy- Weinberg
Equilibrium it must
follow the five
following standards
The population is large
There is no gene flow
Meaning there’s no migration of individuals or gametes
into or out of the population
Mutations do not alter the gene pool
Mating is random
All individuals are equal in reproductive success
Meaning natural selection is not occurring within the
population
When population deviate from
Hardy- Weinberg equilibrium, the
gene pool changes, and evolution
occurs
4 main causes of evolutionary change are:
1) Genetic drift
2) Gene flow
3)Natural selection (only contributes to adaptive
evolution)
4) Mutation (only over time)