BIOL208 Lecture Notes - Lecture 5: Biogeography, Synapomorphy, Chordate
29 Mar 2018
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Document Summary
Variation in populations provides the raw material for natural selection. Some variation within a population of organisms can be inherited. Genotypic: genetic variation among individuals caused by differences in genes or other dna sequences. Phenotype is determined by interaction of environmental factors and organism"s genotype. Not all genotypic variation is expressed (redundancy in genetic code) Sometimes phenotype is determined solely by the environment and is not heritable. Ex: blue hydrangea flowers when grown on acid soils. For natural selection to act on variation, it must be "seen" by the environment (expressed in the phenotype) and be heritable (caused by genotype) Variation in populations is random, but variation is not natural selection (variation is the raw material for natural selection) Selective agent: component of natural environment that consistently causes differential survival and/or reproduction. The intensity with which the selective agent acts on a population to evolve is the selective pressure. There can be no natural selection without selective pressures.
