individuals are selected, but populations evolve population genetics modern synthesis population...
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Individuals are selected, but populations evolve
• Population genetics
• Modern synthesis
• Population• Species• Gene pool
Fir populations Not totally isolated, interbreeding may occur
Eastern U.S. People mobile, but more likely to choose mate locally
• Gene pool – all alleles in a population• Diploid organisms – 2 alleles at each locus• Two or more alleles in a population – each
has a relative frequency (proportion)• Population = 500 organisms = ? alleles• 320 homozygous dominant = ? alleles• 160 heterozygous = ? alleles• 20 homozygous recessive = ? alleles
HARDY - WEINBERGp + q = 1p2 + 2pq + q2 = 1 p = frequency of dominant alleleq = frequency of recessive allele
PKU 1/10,000 births; q2 = ?
Hardy-Weinberg Equilibrium
Very large populationNo migrationNo net mutationsRandom matingNo natural selectionNo genetic drift
Causes of MicroevolutionEvolution is a generation-to-generation
change in a population’s frequencies of alleles.
Genetic Drift – a change in a population’s allele frequencies due to chance bottleneck effect: drastic reduction in population size founder effect: new colony, not representative of the
larger populationNatural Selection – allele frequencies in offspring
generation different than parental due to differential reproductive success
GENE FLOW: genetic change due to migration, tends to reduce differences between populations.
Gene flow & Human Evolution
MUTATION: a change in an organism’s DNA
Quantitative characters - vary along continuum
Discrete characters - either/or
Polymorphism - 2+ forms represented - applies to discrete characters
Gene diversity - average % heterozygous loci
Nucleotide diversity - about 0.01% in humans
Clinal variation
GEOGRAPHIC VARIATION
Madeira: 2 mouse populations separated by mountains
Squirrel populations & the Grand Canyon
• DIPLOIDY – recessive alleles cannot be selected for/against in heterozygotes
• BALANCED POLYMORPHISM– Heterozygote advantage: malaria &
sickle cell anemia– Frequency dependent selection:
survival & reproduction of 1 morph declines if that phenotype becomes too common
• NEUTRAL VARIATION
FREQUENCY DEPENDENT SELECTION IN HOST/PARASITE RELATIONSHIP
Modes of selection
Directional selection
Intermediate selected against – inefficient at cracking both size seeds
Sex: 2 fold disadvantage
Sexual SelectionSexual dimorphism: secondary sex
characteristicsIntrasexual selection: direct competition
among same sex individuals Intersexual selection: mate choice,
individuals of one sex (usually female) are choosy in selecting mates