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Chapter 17

BIOL 1001 Chapter 17: CH 17 Microevolution.docx

Course Code
BIOL 1001
Roberto Quinlan

of 27
CH 17 Microevolution: Genetic Changes
Within Populations 01/20/2013
Penicillium  first antibiotic drug based on a naturally occurring substance
that kills bacteria
Streptococcus pneumoniae: leading cause of infectious death worldwide
12k people in Canada annually need hospitalization
•bacterial populations change in response to antibiotics through the evolutionary process of selection
microevolution example: evolution of antibiotic resistance in bacteria
(heritable change in the genetics of a population)
population: all the individuals of a single species that live together in the same place and time
•natural selection can change the pattern of variation in a population from one generation to the next
microevolutionary change results from several processes, not just natural selection, sometimes processes
counteract each other
17.1 Variation in Natural Populations
phenotypic variation: differences in appearance or function that are passed from generation to
biochemistry / physiology / internal anatomy / behaviour
17.1a Evolutionary Biologists Describe and Quantify Phenotypic Variation
•microevolutionary studies often begin by assessing phenotypic variation within populations
quantitative variation: individuals differ in small, incremental ways.
Ex. Mass of humans varies almost continuously from lightest to heaviest
Ex. Humans exhibit quantitative variation in length of toes, number of hairs, and height
•width of curve proportional to variability, mean describes average value of the character
natural selection changes mean value of a character or its variability within populations
qualitative variation: (Mendel) exist in two or more discrete states, and intermediate forms are often
polymorphism: existence of discrete variants of a character
such traits are described as polymorphic
biochemical polymorphisms  human A, B, AB, O blood groups
•describe phenotypic polymorphisms quantitatively by calculating the percentage or frequency of each trait
17.1b Phenotypic Variation Can Have Genetic and Environmental Causes
Phenotypic variation within populations may be caused by genetic differences between
individuals, by differences in the environmental factors that individuals experience, or by
an interaction between genetics and the environment.
Result genetic and phenotypic variations may not be perfectly correlated
•organisms with different genotypes can exhibit the same phenotype
ex. Black mice from Arizona or black mice from Mexico
•organisms with same genotypes can exhibit different phenotype
ex. Acidity in soil (color of plant)
•must know if phenotypic variation is caused by genetic differences, environmental factors, or an interaction
of both
•••only genetically based variation is subject to evolutionary change•••
because environmental factors can influence the expression of genes, an organism’s phenotype is
frequently the product of an interaction between its genotype and its environment
how to test environmental cause  change variable and use same genes
•breeding experiments can demonstrate the genetic basis of phenotypic variation
traits that vary quantitatively will respond to artificial selection only if the variation has some genetic basis