BIOL 226 Lecture Notes - Lecture 2: Sickle-Cell Disease, Allele Frequency, Gene Pool
3 May 2018
School
Department
Course
Professor
Biol226- Ch23
The Evolution of Populations
Natural selection acts on individuals
Adaptive evolution
evolution that results in a better match between organisms and their environment
Microevolution
evolution on smallest scale
change in allele frequency in a population over generations
Mechanism that cause allele frequency change:
i) Natural selection
ii) Genetic drift: change in allele frequency by chance
iii) Gene flow: transfer of allele between populations
Genetic variation phenotypic variation, differences among individuals in the composition of their genes
or DNA sequence
Sources of genetic variation
i) Formation of new alleles (mutation)
ii) Change in number or position of genes
iii) Rapid reproduction
iv) Sexual reproduction
geographic variation
differences in the genetic composition of separate populations
Mutation
New alleles can rise by mutation
Point mutation: change of one base in a gene
Sickle cell disease
Heterozygote protection: In diploid organism, harmful alleles can hide in heterozygosis maintaining
huge pool of none favorable alleles
Change in number or position of genes
Independent assortment of chromosome:
Crossing over
fertilization
Chromosomal rearrangement is usually harmful
Rapid reproduction
Mutation rate is lower in prokaryotes but they have more generation per unit of time mutation
generates genetic variation quickly in the population
Population
Group of individuals of the same species living in the same area and interbreeding
Gene pool
All copies of every type of allele at every locus in all members of population
Hardy-Weinberg equilibrium
A population that is not evolving allele and genotype frequencies will
remain constant
Conditions:
i) No mutations
p2 +2pq+ q2 =1
Document Summary
Evolution that results in a better match between organisms and their environment. Change in allele frequency in a population over generations. Mechanism that cause allele frequency change: natural selection, genetic drift: change in allele frequency by chance, gene flow: transfer of allele between populations. Genetic variation phenotypic variation, differences among individuals in the composition of their genes or dna sequence. Sources of genetic variation: formation of new alleles (mutation, change in number or position of genes, rapid reproduction, sexual reproduction. Differences in the genetic composition of separate populations. Point mutation: change of one base in a gene. Heterozygote protection: in diploid organism, harmful alleles can hide in heterozygosis maintaining huge pool of none favorable alleles. Change in number or position of genes. Mutation rate is lower in prokaryotes but they have more generation per unit of time mutation generates genetic variation quickly in the population. Group of individuals of the same species living in the same area and interbreeding.
