PROCESS OF EVOLUTION I
(Genetic Context)
Since the Time of Darwin
 Darwin did not explain how variation originates or passed on
 The genetic principles were recently applied to populations to
explain how evolution occurs
 Evolution: changes in the genotype & phenotype of
populations overtime
Microevolution
 Gene pool: all alleles found in a population
 Microevolution: a change in the gene pool of a population
from generation to generation
 Allelic frequency: number of alleles (in question) divided by
the total number of alleles in the gene pool
 Genotypic frequency: the number of a specific genotype
divided by the total number of genotypes in the population
 A change in allelic & genotypic frequencies are used to
measure evolution
Hardy-Weinberg Equilibrium
 They recognized that allelic frequencies in a gene pool will
remain constant over time if certain conditions were met:
1. No mutation
2. No gene flow (No migration)
3. Random mating
4. No genetic drift (population is large)
5. No selection (all genotypes are equally important)
 If these conditions are met there will be no evolution
 The last two are the main causes of evolution
Calculating genotypic & Phenotypic Frequencies
 The population under study is sampled
 Using electrophoresis: alleles, homozygous dominant &
recessive, and heterozygous were determined
 Using the equations below, conclusion were made on evolution
 Calculating Frequencies Using Hardy-Weinberg Equations
Allelic frequency: p + q = 1
Genotype frequency: p2 + 2pq + q2 = 1
Causes of Microevolution
 Deviations from Hardy-Weinberg conditions can result in
genetic changes that lead to evolution
Gene Flow
 Gene flow: movement of alleles between interbreeding
adjacent populations
 Introduce new genes in a population
 Continuous gene flow makes the gene pool of populations
similar preventing evolution
Nonrandom Mating
Deviations from random mating:
 Inbreeding:
It increases both homozygous dominant & recessive
 Assortative mating: favors similar phenotypes
It divides the population into two or more phenotypes
 Sexual selection: e.g., female chose their mates
Genetic Drift
 Genetic drift: a random process that results in changes
of allele frequencies
It occurs more frequently in small populations
 Bottleneck effect: genetic drift that occurs when only
few individuals of a population remains
Populations carry only a fraction of the original genes
Each individual in the population become important. why?
Founder Effect
(an example of genetic drift)
 A founder is one or few individuals separated by geographical
barriers from the main population
 The founder population carries only a small fraction of the
genetic diversity in the original population
 Genetic drift in the new colony is called a founder effect
 It is a condition where rare alleles occur at higher frequencies