Weeks 1 and 2 Flashcards
Genetic drift
Natural selection
Mutation
Migration
evolutionary forces that can cause change in allele frequency from one generation to another
Population genetics looks at
changes in gene frequency within and between populations
Microevolution
evolution within a species
Ho for population genetics
no evolution
P =
relative frequency of A1A1 genotype (normal homozygotes)
of A1A1 individuals / total population number
H =
relative frequency of A1A2 genotype (heterozygotes)
of A1A2 individuals / total population number
Q =
relative frequency of A2A2 genotype (recessive)
of A2A2 individuals / total population number
Relative frequency of A1 allele
p = P + 1/2H
Relative frequency of A2 allele
q = Q + 1/2H
When is a locus being in HWE?
when no forces of evolution influence allele frequencies at a single gene locus.
Consequences of being in HWE?
a gene locus is said to be in HEW
allele frequencies will predict genotype frequencies
genotype frequencies will remain stable
allelic variation is NOT lost between generations
Rare alleles are maintained in heterozygotes
HWE is a property of
a gene NOT an individual or a population
Genes are acted upon
by evolutionary forces
In a population some genes are in HWE and some are not
True
Assumptions of HWE
- Large population size (insures no genetic drift)
- No external forces ( no nat. sel, mutation, migration)
- Random mating (no assortive mating, sexual selection or inbreeding)
What genes tend to be in HWE
those with phenotypes that have no positive or negative effects
Called selectively neutral loci
When is the frequency of heterozygotes the highest
When p and q are equal (each at 0.5)
How quickly can a locus reach HWE?
within one generation of random mating
Multiple alleles with HWE
(p+q+r)2
Sex-linked traits with HWE
in males p=P and q=Q because males are hemizygous
Use male values to find females:
Females: p2=P, 2pq=H, q2=Q
When looking at numerical values, what indicates a population is NOT in HWE?
deviations of observed genotype from expected genotype = evolution
Why is HWE important to genetics?
Provides a starting point to test for evolution within a population.
If locus is not in HWE, then evolution must be acting on that locus
Next step….determine which evolutionary force is at work
Evolution acts on what
natural variation within a population
define selection
directed variation in survival and reproduction of different types.
Can be beneficial or harmful (causes directional selection)
Define genetic drift
Random variation due to segregation and independent assortment
Macroevolution
speciation. phenotypes become so different that species cannot reproduce together
What are the geologic pieces of evidence supporting evolution?
Fossil layers Radiometric dating Principle of superposition Principle of cross - cutting relationships Principle of faunal succession
What evidence for evolution comes from the fossil record
extinction
succession
transitional forms
What evidence for evolution comes from common ancestry
Homologous structures: arise from common origin / common embryonic development
Homologies that are NOT analogies provide strongest support
Genetic homology
Vestigial structures
Convergent evolution leads to
Analogous structures. NOT evidence of a common ancestor. Evolve independently due to similar environmental pressures.
