BIOLOGY 12 Evolution - Evolution of Populations - Disruptions to Equilibrium - Coevolution - Pace - New Species

Evolution of Populations - Mechanisms population – localized groups of individuals belonging to the same species gene pool – all of the genes present in a species population gene (allele) frequency – proportion of each gene (allele) in the gene pool genetic equilibrium – stability of the frequency of genes in successive generations of a population

Evolution of Populations… natural selection has an effect only on the phenotype of an organism therefore heterozygote genotypes preserve recessive genes in populations and variety is conserved *if frequencies change, equilibrium is broken and evolution occurs*

Disruptions to equilibrium are caused by: 1) mutations 2) genetic drift – changes in the gene pool of a population due to chance two types: A) bottleneck effect – genetic drift that results from a sudden decrease in population due to environmental factors (fire, flood etc.) B) founder effect – genetic drift that results from a small population colonizing a new area

Bottleneck Effect

Example of a Bottleneck Northern Elephant Seals population reduced to as few as 20 individuals (due to hunting) population has now recovered to over 30 000 but little genetic variation

Disruptions to equilibrium continued… 3) gene flow (migration) – the loss or gain of alleles from a population due to the migration of fertile individuals or the transfer of gametes between a population

Coevolution when two or more species influence each others evolution examples: flowering plants and their pollinators predator prey relationships (newts) leaf cutter ants and fungi humans and symbiotic bacteria humans and pathogenic bacteria (resistant TB)

Pace of Evolution two theories: 1) gradualism: states that populations slowly diverge from one another by the accumulation of adaptive characteristics within a population *if this theory is correct, we would expect to find many intermediate forms of species within the fossil record; scientists have found intermediate forms of only a few species, but some argue this is due to an incomplete fossil record

Pace of Evolution continued… 2) punctuated equilibrium: evolution proceeds with periods of inactivity (with little or no change) followed by very active phases, so that major adaptations or clusters of adaptations appear suddenly in the fossil record *this is supported by species who have not evolved in millions of years and others that have changed a lot within the last ~50 000 years

How do new species arise? Divergent evolution: evolution in which related species progressively differentiate a major type of divergent evolution is Adaptive radiation: the emergence of numerous species from a common ancestor introduced to an environment presenting a diversity of new opportunities and problems

Textbook Questions 1 – page 518 1 – page 528 7 – page 533 10 and 16 – page 540 1,3,4 and 5 – page 555 4 – page 605