Chapter 17: Population Genetics and Evolution
Population Genetics
deals with the abundance of different alleles within a population and the manner in which the abundance of a particular allele increases, decreases, or remains the same with time.
Factors that Cause the Gene Pool to Change
Mutation
Artificial Selection
Natural Selection
because of mutation, existing alleles decrease in frequency, and new alleles increase
the most significant factor causing gene pool changes; usually described as survival of the fittest
the process in which humans purposefully change the allele frequency of a gene pool
also used to produce ornamental plants that flower more abundantly or for a longer time
often carried out in conjunction with artificial mutation
two conditions must be met before natural selection can occur
whether or not mutation is significant depends in part of on the population's size
does not include purpose, intention, planning, or voluntary decision
Rates of Evolution
Speciation
natural selection has caused a new species to evolve, a process called speciation
can occur in two fundamental ways:
Phyletic Speciation
Divergent Speciation
This movement of alleles physically through space, called gene flow, occurs in many ways, such as by pollen transfer, seed dispersal, and vegetative propagation
Abiological Reproductive Barriers
Biological Reproductive Barriers
Adaptive Radiation
a special case of divergent evolution in which a species rapidly diverges into many new species over just a few million years
any biological phenomenon that prevents successful gene flow
any physical, nonliving feature that prevents two populations from exchanging genes
Evolution and the Origin of Life
there are many species of seedless plants (lycopods, Equisetum, ferns) that have persisted for tens of millions of years without diverging into new species
the most seriously considered hypothesis about the origin of life on Earth is that of chemosynthesis
prezygotic isolation mechanisms
neither pollination nor fertilization occurs