Ch. 19 Evolution of populations
Genetic variation makes evolution possible:
Microevolution= change in allele frequency in a population over generations
Population genetics= studies how some selective forces impact populations through changes in
in allele and genotype frequencies
3 main mechanisms cause allele frequency change
o Natural selection
o Genetic drift
o Gene flow
Only natural selection consistently causes adaptive evolution
Variation in heritable traits is a pre-req for evolution by natural selection:
Allele frequency= rate at which a specific allele appears within a population
Every phenotypic change is the result of genetic change
A change in phenotypic frequency over time would constitute evolution in the population
The allele frequency can change due to environmental factors
Formation of New Alleles:
New alleles arise by mutation, a change in the nucleotide sequence of DNA. A “point mutation”
is a change of a single nucleotide in a DNA sequence
Only mutations in cells that produce gametes can be passed to offspring
Altering Gene Number or Position:
Chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful
Duplication of large chromosome segments is generally harmful, but duplication of small pieces
of DNA may not be
Duplicated genes can take on new functions by further mutation
Mutation Rates:
Mutation rates are generally low in animals and plants
Average is about one mutation in every 100,000 genes per generation
Mutation rates are often lower in prokaryotes, but high generation rates allow mutations to
accumulate rapidly
Viruses are also able to accumulate mutations rapidly due to their short generation times
Mutation rates are faster in viruses as hosts lack RNA repair mechanisms
Sexual Reproduction:
In organisms that reproduce sexually, most genetic variation results from recombination of
alleles
Sexual reproduction can shuffle existing alleles into new combinations through 3 mechanisms
o Crossing over
o Independent assortment
Genetic variation makes evolution possible:
Microevolution= change in allele frequency in a population over generations
Population genetics= studies how some selective forces impact populations through changes in
in allele and genotype frequencies
3 main mechanisms cause allele frequency change
o Natural selection
o Genetic drift
o Gene flow
Only natural selection consistently causes adaptive evolution
Variation in heritable traits is a pre-req for evolution by natural selection:
Allele frequency= rate at which a specific allele appears within a population
Every phenotypic change is the result of genetic change
A change in phenotypic frequency over time would constitute evolution in the population
The allele frequency can change due to environmental factors
Formation of New Alleles:
New alleles arise by mutation, a change in the nucleotide sequence of DNA. A “point mutation”
is a change of a single nucleotide in a DNA sequence
Only mutations in cells that produce gametes can be passed to offspring
Altering Gene Number or Position:
Chromosomal mutations that delete, disrupt, or rearrange many loci are typically harmful
Duplication of large chromosome segments is generally harmful, but duplication of small pieces
of DNA may not be
Duplicated genes can take on new functions by further mutation
Mutation Rates:
Mutation rates are generally low in animals and plants
Average is about one mutation in every 100,000 genes per generation
Mutation rates are often lower in prokaryotes, but high generation rates allow mutations to
accumulate rapidly
Viruses are also able to accumulate mutations rapidly due to their short generation times
Mutation rates are faster in viruses as hosts lack RNA repair mechanisms
Sexual Reproduction:
In organisms that reproduce sexually, most genetic variation results from recombination of
alleles
Sexual reproduction can shuffle existing alleles into new combinations through 3 mechanisms
o Crossing over
o Independent assortment
