Evolutionary Processes
Monday, February 28, 2022 10:04 AM
• Evolution
○ Change in the genetic characteristics if a population over time
• Change in genetic characteristics
○ Change in allele frequencies within a population
• Allele
○ A particular version of a gene
• Alleles -> genotypes -> phenotypes
○ A and a - alleles (versions of genes) ->
○ AA, Aa, aa - genotypes (combination of all alleles possessed by
individuals ->
○ Phenotypes (observable traits)
• Evolution is a change in allele frequencies of a population over time and it can
be caused by:
○ Natural selection
§ That includes:
□ Balancing
□ Directional
□ Stabilizing
□ Disruptive
○ Genetic drift
§ Causes allele frequencies to change randomly and can lead to loss
of diversity
○ Gene flow
§ Occurs when individuals leave one population, join another, and
breed. Makes allele frequencies more similar between populations
○ Mutations
§ Modifies allele frequencies by continually introducing new alleles
○ Hardy Weinberg Principle
§ A very simplified model can be used to test whether evolution is
acting on a particular gene in a population
§ Gen 1 (diploid) -> gene pool (haploid genes) -> gen 2 (diploid)
§ The hardy Weinberg principle serves as a null hypothesis for
determining whether evolution is acting on a particular gene in a
, determining whether evolution is acting on a particular gene in a
population
§ H0 = evolution is not occurring = hardy Weinberg equilibrium
§ H1 = evolution occurring
§ 5 assumptions of hardy Weinberg principle
□ No natural selection
□ No genetic drift
□ No geneflow
□ No mutation
□ Random mating
§ Two fundamental claims
□ If the frequencies of alleles A1 and A2 in a population are given
by p and q, then the frequencies of genotype A1A1, A1A2, and
A2A2 will be given by p2, 2pq, and q2 for the generation after
generation
□ When alleles are transmitted, their frequencies do not change
over time. For evolution to occur, some other factor (s) must
come into play
§ p2 + 2pq + q2 = 1 <- hardy-Weinberg equation
§ Process overview
□ Observed genotype frequencies -> A1A1, A1A2, A2A2
□ Observed allele frequencies -> A1, A2
□ Expected -> A1A1 = p^2, A1A2 = 2pq, A2A2 = q^2
§ Hardy-Weinberg equilibrium: how to calculate frequencies
□ p= frequency of the dominant allele in the population
□ q = frequency of the recessive allele in the population
□ p2 = percentage of homozygous dominant individuals
□ q2 = percentage of homozygous recessive individuals
□ 2pq = percentage of heterozygous individuals
□ p2 + 2pq + q2 = 1
□ p+q=1
• Nonrandom mating
○ Inbreeding: Mating between two relatives
§ Most intensively studied form of nonrandom mating
○ Two Fundamental points
§ Inbreeding increases homozygous
§ Inbreeding itself does not cause evolution because allele
frequencies do not change the population as a whole
• How does inbreeding influence evolution?
Monday, February 28, 2022 10:04 AM
• Evolution
○ Change in the genetic characteristics if a population over time
• Change in genetic characteristics
○ Change in allele frequencies within a population
• Allele
○ A particular version of a gene
• Alleles -> genotypes -> phenotypes
○ A and a - alleles (versions of genes) ->
○ AA, Aa, aa - genotypes (combination of all alleles possessed by
individuals ->
○ Phenotypes (observable traits)
• Evolution is a change in allele frequencies of a population over time and it can
be caused by:
○ Natural selection
§ That includes:
□ Balancing
□ Directional
□ Stabilizing
□ Disruptive
○ Genetic drift
§ Causes allele frequencies to change randomly and can lead to loss
of diversity
○ Gene flow
§ Occurs when individuals leave one population, join another, and
breed. Makes allele frequencies more similar between populations
○ Mutations
§ Modifies allele frequencies by continually introducing new alleles
○ Hardy Weinberg Principle
§ A very simplified model can be used to test whether evolution is
acting on a particular gene in a population
§ Gen 1 (diploid) -> gene pool (haploid genes) -> gen 2 (diploid)
§ The hardy Weinberg principle serves as a null hypothesis for
determining whether evolution is acting on a particular gene in a
, determining whether evolution is acting on a particular gene in a
population
§ H0 = evolution is not occurring = hardy Weinberg equilibrium
§ H1 = evolution occurring
§ 5 assumptions of hardy Weinberg principle
□ No natural selection
□ No genetic drift
□ No geneflow
□ No mutation
□ Random mating
§ Two fundamental claims
□ If the frequencies of alleles A1 and A2 in a population are given
by p and q, then the frequencies of genotype A1A1, A1A2, and
A2A2 will be given by p2, 2pq, and q2 for the generation after
generation
□ When alleles are transmitted, their frequencies do not change
over time. For evolution to occur, some other factor (s) must
come into play
§ p2 + 2pq + q2 = 1 <- hardy-Weinberg equation
§ Process overview
□ Observed genotype frequencies -> A1A1, A1A2, A2A2
□ Observed allele frequencies -> A1, A2
□ Expected -> A1A1 = p^2, A1A2 = 2pq, A2A2 = q^2
§ Hardy-Weinberg equilibrium: how to calculate frequencies
□ p= frequency of the dominant allele in the population
□ q = frequency of the recessive allele in the population
□ p2 = percentage of homozygous dominant individuals
□ q2 = percentage of homozygous recessive individuals
□ 2pq = percentage of heterozygous individuals
□ p2 + 2pq + q2 = 1
□ p+q=1
• Nonrandom mating
○ Inbreeding: Mating between two relatives
§ Most intensively studied form of nonrandom mating
○ Two Fundamental points
§ Inbreeding increases homozygous
§ Inbreeding itself does not cause evolution because allele
frequencies do not change the population as a whole
• How does inbreeding influence evolution?
