SBI3U: Evolution
Evolutionary Mechanisms
Date: ______________


Gene pool: _____________________________________________________________________
Allele frequencies: ______________________________________________________________

_______________________ occurs when the allele frequencies of a population change over time.
1. Small vs. Large Populations

___________________________: When a population is small,
__________ fluctuations can cause changes in allele frequencies.
 Could become the __________________________ of the species.
 Could be __________________________.

_____________________________: ________________________
in numbers, ______________________ of alleles ______________,
new generation different from original
o Northern elephant seal (reduced to 20 individuals in
1890s…)

______________________: a few individuals ______________________________________
population
Ex. Seeds/insects carried by wind, birds to
another________________



Self-pollinating plants
Amish community in Pennsylania (30 emigrants from Switzerland, 1720)
_______________________ in the Galapagos (1982-1983, a new
population developed – discovered by scientists at Queen’s)
2. Non-Random Mating: When mating opportunities are nonrandom,
individuals that are ______________________ _______________ will pass
on their alleles in _______________________ than less preferred mates.
3.
Genetic mutations create _______________________ or _______________________________
into another, thereby changing the __________________________ of both
alleles.
 _________________________ are the main source of new genetic
material, as extra copies they are free to mutate with less likelihood of
causing harm.

Mutations occur as 1 in 10000 in a small genome (bacteria) to about 1 or more per gamete in
larger genome.
4. Migration: When individuals migrate, this ___________________________________ of both the
population it __________and the one it ____________.
 ___________________: movement of alleles from one population to another.
 Tends to _______________ differences between populations
5. When natural selection occurs, individuals with certain alleles have
____________________ _____________________________than others
do, thereby ____________________the relative frequency of their
alleles in the next generation.
 Harmful genes selected ________________
 Useful genes _______________
Homework:
1) Define evolution using the term allele frequency
2) What is the difference between genetic drift and gene flow? Give an example of each.
3) “The northern elephant seal population was reduced by overhunting to 20 individuals in the
1890s. Although the population had rebounded to over 30 000 individuals by 1974, genetic
testing revealed limited genetic variation amoung the population.” What evolutionary
mechanism is this an example of? Explain why the seal population in 1974 lacked genetic
variation.
4) Give three examples of species that may produce founder populations.
5) During the fall migration, several Canada geese stop over at a river near a good food source and
then nest there the following spring. Because of the abundance of food, this population of
geese stops migrating. What effects, both immediate and long-term, might this situation have
on the gene pools of original and founder populations?
6) Which evolutionary mechanism results in new genetic information?