Hardy-weinberg Equilibrium Flashcards
Allele frequency
Frequency of a particular allele in population.
-population fundamental unit of evolution
Genetic basis
For evolution to occur, genetic differences must account for phenotypic differences
Natural selection
Favors traits most adaptive under present environment (better foragers or better camoflouged or avoid predation)
Ever-changing environment
- individuals must MIGRATE, ADAPT, DIE
- natural selection acts on existing variations
- environment never creates favorable alleles
New alleles arisen by
Mutation and genetic drift , gene flow, nonrandom mating
Gene flow( when individuals disperse) alters allele frequency
Mutation
Changes in DNA base sequence
Genetic drift
Random changes in allele frequencies without regard to adaptation
Ex: elephant seals
Large population becomes small and increased to large
GENETIC BOTTLENECK: large-reduced-large)
-allele frequency is altered due to population crash
-small populations have big effect
-genetic drift inversely related to population size
Change in heritable characteristics
Consequence of change allele frequencies
-all evolutionary change is described as sequential origin of new alleles, their replacement of old ones and occasionally the origin of New through duplication or lateral transmission from another lineage leading to insertion. (By virus)
Hardy-Weinberg equilibrium
-situation where no evolution is occurring
-genetic equilibrium
-allele frequency will not change:
No natural selection
No mutation
No genetic drift (no infinte population size)
No allele flow
Random mating
-how a particular genotype will become more or less common over time
Phenotype frequency
Proportion of individual exhibiting observable traits
-#indiv with phenotype/ total
Genotype frequency
Proportion of genotypes at a given locus
-Indiv with genotype/ total
Allele frequency
Proportion of alleles at a given locus
-p= freq. dominant allele
-q= freq. recessive allele
Allele frequencies from number of individuals
- p= ((#AA + 1.5(#Aa))/ N
- q= ((#aa) + 1.5(#Aa))/N
N=total
Genotype freq. to allele freq.
P= f(AA) + 1.5(f(Aa))
q= f(aa) + 1.5 (f(Aa))
TO GO FROM ALLELE TO GENOTYPE MUST ASSUME HW EQUIL
Genotype to allele
AA= p^2
Aa=2pq
aa=q^2
P^2+2pq+q^2=1.0
In order to be in hardy Weinberg
Allele frequency must predict genotype frequency
Two processes that generate variation
- Mutation: ultimate source of new genes
Create different versions of alleles - Genetic recombination: this results in new recombinations of genes
Genetic drift
Occurs when founders start a new population or after a genetic bottleneck with interbreeding
- endangered species go thru genetic bottleneck so suffer from reduced genetic variation
- small populations
Founder effect
When founders contain a fraction of total genetic diversity of original population
Ex: grey seals in Britain,
-metapopulation to increase genetic variation
Ex: island of Tristan da cunha
-founded by britons. One had allele for blindness, among their defenders 4 are blind and 9 carriers
Ex: Amish population pen
-closed community
-genetic disease higher than in German population
-sheer chance
Neutral theory of molecular evolution
Mooto Kimura
2 observations:
-Excessive amounts of protein polymorphism
-Molecular clock
Refers to apparent constant rate of protein evolution over large periods of time
Kimura: clock reflects action of random drift not selection
New alleles
- origin through spontaneous mutation of a single nucleotide within sequence
- single cell: immediately new allele and subject to drift
- multi cell: nucleotide substitution must arise within germ line that gives rise to gametes
- most alleles lost to genetic drift but occasionally become more common and random accident replaces.
Natural selection…
Is not same as evolution
Different from evolution by natural selection
No efect unless diff phenotypes also differ in genotype
Variation in average reporoductive success (including survival) among phenotypes.
three principles of Darwin evolution
Competition, sturggle for exisistence
Heritable variation
Heritability, variation matters in struggle
Survival and reproduction are not random. Must be correlation between fitness and phenotype
People wanted life itself to be purposeful and creative
Neo-Lamarckism
Orthogenesis
Mutationism
Inheritance of acquired characteristics
Variation that arises is directed toward a goal
Discrete variations are all that matter
