January 17, 2014
Sources of biological variation:
♦ Mutations: are the only new sources of alleles in a species
♦ Sexual Reproduction: recombines the parents’ DNA to form new combinations
♦ Random Mating: is a process whereby every allele has an equal chance of being
passed on to the next generation
♦ Natural Selection: acts on this variation by differential reproductive success.
♦ Adaptation: Any change by which organisms respond to selection pressure
♦ Genetic Adaptations: are changes within populations in response to selection
pressure (over several generations); applies only to populations.
♦ Acclimatization: is a physiological response within individuals to environmental
pressure (takes from a few days to a few months) usually not permanent. Eg. Tanning
in humans to protect our skin from UV rays. Is not genetic.
o Primary sources of new biological variation are recombination and
♦ Migration (Gene flow): the movement of alleles from one population to another as a
result of interbreeding. **Makes population more similar to each other; share
more alleles in common. In each individual population group they are more
different from each other; since new allele was introduced, greater genetic
♦ Genetic Drift: A change of allele frequencies as a consequence of random changes
in a population size. (Reduces allele frequencies, so future generations have more
things in common, and become much more similar to each other)
♦ **The migration of small subpopulation away from the parent population (Founder
effect) (causes more differences between two original populations because they
become genetically different) (Small population’s descendants are going to be
more similar because of less alleles being present)
♦ The removal of a large portion of the population because of a natural disaster
(bottleneck effect) Left with a small population, there are less alleles present, so the
population becomes more similar to each other.
♦ Species: are group of individuals that can interbreed and produce fertile offspring.
♦ Speciation can occur through geographic isolation, natural selection and/or
reduction of gene flow.
Mapping Biological Diversity:
♦ Human population differ in the frequency of alleles, not by the presence or absence of
♦ While some alleles produce discrete variation, ma