AP Biology – Ch. 23 – The Evolution of Populations The smallest unit of evolution? Microevolution 3 main mechanisms responsible for change in allele frequency Which one of these consistently improves the match between organisms and their environment?
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AP Biology – Ch. 23 – The Evolution of Populations The smallest unit of evolution? Microevolution 3 main mechanisms responsible for change in allele.
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AP Biology – Ch. 23 – The Evolution of Populations
The smallest unit of evolution? Microevolution 3 main mechanisms responsible for change in
allele frequency Which one of these consistently improves the
How do the variations that are the raw material for evolutionary change arise?
Mutation and sexual reproduction
Genetic Variation
A) Variation Within a Population
Discrete or quantitative Either-or-basis vs on a continuum Single gene vs two or more genes
Measuring Genetic Variation
Gene variability vs nucleotide variability
Average heterozygosity – gel electrophoresis, restriction fragment analysis
Nucleotide variability – compare DNA sequences
Why is this information important?
Variation between populations
Geographic variation-differences in the genetic composition of separate populations
Ex) mice populations separated by a mountain range, mummichog fish and a cold-adaptive allele(cline)
Mutation
The ultimate source of new alleles Change in the nucleotide sequence
of an organism’s DNA Point mutation Alter gene number or sequence
Mutation rates – low in plants and animals
- even lower in prokaryotes and viruses(but shorter generation time)
- RNA viruses – mutations accumulate faster – how does this impact treatment?
Sexual Reproduction
variation results from the unique combination of alleles that each individual receives due to:
- crossing over - independent assortment - fertilization
23.2 – Hardy-Weinberg
-population-gene pool/fixed allele-conditions for HW equilibrium? 1. no mutations 2. random mating 3. no natural selection 4. extremely large population 5. no gene flow
23.3
Natural selection, genetic drift, and gene flow – alter allele frequencies directly
1. natural selection – favoring some alleles over others can result in adaptive evolution