Microevolution – BioH Ch 16. Where did all organisms come from? Why such variety?. Early Beliefs. Supernatural intervention (BC & early AD) “Gods” Naturalism (1300’s) Chain of Being “Small” known world, small number of species World exploration led to many more species. 16.1.
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Where did all organisms come from?
Why such variety?
many more species
organisms based on
Depends upon five factors:
Stable allele frequencies = “genetic equilibrium”
NOT exhibiting evolution
All five factors do not usually happen at the same time
Changes in combinations of alleles lead to variations in a populations’ phenotypes. (This could be structural, functional and/or behavioral changes).
MICROEVOLUTION refers to small-scale changes in allele frequencies as caused by mutations, gene flow & genetic drift. These all shuffle alleles into, through or out of populations.
Allele mutations can be lethal, neutral or beneficial.
Gene flow involves the natural movement of individuals into, through or out of a population – moving their specific alleles with them.
Genetic drift is the natural, random change in allele frequencies over time caused by chance alone
Natural Selection = an outcome (result) of the differences in survival and reproduction among individuals that show variation in heritable traits.
With time, natural selection can lead to increased fitness (better adaptation to the environment).
Allele frequencies change in one
direction in response to environmental changes or changes caused by
Pre-Industrial Revolution – light moths common on light tree trunks and darks moths were rare
Post-Industrial revolution – moth population depended upon how close the trees were to an industrial site (and soot)
Stabilizing selection – forms of a trait are favored by environment conditions. The trait becomes prominent
Disruptive selection – the intermediate form of the trait is NOT favored. The extreme forms of the trait become prominent
male and female phenotypes
resulting in selective breeding
In small populations, genetic drift may lead to a homozygous condition with the loss of genetic diversity