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Lesson 25 – Evolutionary
Processes
Life Science
1
Lesson 25
• Look at the structures in this lesson.
• Can also look this website on mechanisms
of evolution
2
Mechanisms of Evolution
• Change in how
common a gene is in
a population (gene
frequency).
• Can result from gene
flow, non-random
mating, genetic drift,
mutation and natural
selection.
3
Gene Flow (Migration)
• Movement of genes from one population to
another.
(Image from http://evolution.berkeley.edu/evosite/evo101/images/beetles_mech2.gif)
4
Nonrandom Mating
• The probability that two
individuals in a population will
mate is not the same for all
possible pairs of individuals.
• The result is that some individuals
have more opportunity to mate
than others and thus produce
more offspring (and more copies
of their genes) than others.]
5
(Image from http://biology.unm.edu/ccouncil/Biology_203/Images/PopGen/nonrandom.jpeg)
Genetic Drift
• Random changes in gene frequency.
• Occurs when some individuals, just by chance,
leave behind a few more descendents (and
genes) than other individuals. The next generation
will be the genes of the “lucky” individuals, not
necessarily the healthier or “better” individuals.
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(Image from http://evolution.berkeley.edu/evosite/evo101/images/beetles_mech3.gif )
Mutation
• Change in DNA.
• Mutations add to the genetic variability of
populations over time.
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Natural Selection
• Individuals having characteristics that aid their
survival will produce more offspring. As a result
the proportion of their genotype will increase in
the population over time.
8
(Image from http://www.answersingenesis.org/assets/images/articles/nab/h-pylori.jpg)