3 Main Questions:
- What is microevolution?
Evolutionary change below the species level; change in the allele frequencies in a population over generations.
- What is mutation?
A change in the nucleotide sequence of an organism's DNA, ultimately creating genetic diversity. Mutations also can occur in the DNA or RNA of a virus.
- What is a gene pool?
The aggregate of all of the alleles for all of the loci in all individuals in a population. The term is also used in a more restricted sense as the aggregate of alleles for just one or a few loci in a population.
5 Main Facts:
- Character that vary within a population may be discrete or quantitative.
- Average heterozygosity is often estimated by surveying the protein products of genes using gel electrophoresis.
- Nucleotide variability is measured by comparing the DNA sequences of two individuals in a population and then averaging the data from many such comparisons.
- Chromosomal changes that delete, disrupt, or rearrange many loci at once are almost certain to be harmful.
- In organisms that reproduce sexually, most of the genetic variation in a population results fromthe unique combination of alleles that each individual receives.
Diagram:
The small wildflower population has a stable size of ten plants. Suppose that by chance only five plants (those in white boxes) of generation 1 produce fertile offspring. This could occur, for example, if only those plants happened to be grow in a location that preovided enough nutrients to support the production of offspring. Again by chance, only two plants of generation 2 leave fertile offspring. As a result, by chance alone, the frequencies of the a allele first increases in generation 2, then falls to zero in generation 3.
Summary:
One common misconception about evolution is that individual organisms evolve. Focusing on evolutionary change in populations, we can define evolution on its smallest scale, called microevolution, as change in allele frequencies in a population over generations.
Natural selection is not the only cause of microevolution. In fact there are three main mechanisms that can cause allele frequencies change: natural selection, genetic drift(chance events that alter allele frequencies), and gene flow (the transfer of alleles between populations).
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