Transcript Modern Evolutionary Theory

Modern Evolutionary Theory
Darwin and Mendel
Supports Darwin’s concepts of variation and
natural selection
 Explains the genetic basis for variations
 Variations can give individuals an advantage
over others in their struggle for resources; any
trait that helps an organism survive and
reproduce is said to have adaptive (survival)
value (example snowshoe bunnies, polar
bears)

2 Ways Variation Occurs
Variation is caused by segregation
(separation of chromosomes into
different gametes) and recombination
(crossing over) during meiosis. In other
words, variation is caused by sexual
reproduction.
 Variation is also caused by mutations
which are changes in the genetic
material.

Chunk!
How is the Modern Theory of Evolution
different from Darwin’s?
 What does “adaptive value” mean?
 What are two causes of variation?
 Define segregation.
 Define recombination.

Natural Selection and Resistance


Natural selection can also be responsible for insects
developing resistance to insecticides.
For example, a few roaches in a population may have
a random mutation
Random mutation does not
have adaptive value in regular
environment…
Resistance
…That allows them to live unaffected when an
insecticide is sprayed. The other roaches in the
population without this mutation would die.
Resistance

Since this mutation makes the bugs more fit for their
environment (one that includes a pesticide), these
roaches live and reproduce, passing the resistance to
their offspring.
Resistance

Note: the insecticide did not CAUSE the resistance. It
just acted as a selecting agent showing which roaches
were more “fit”.
Evolution?

Compare the traits of the original
population and the surviving population.
original
surviving
Resistance

The development of penicillin-resistant strains of
bacteria occurs in a similar fashion
Chunk!

Why was there variation in the original population?
 What was the effect of the mutation without spray
present?
 What is the effect of the mutation with spray present?
 Why is saying the roaches are “immune” to the spray
incorrect?
 What is the proper term?

What caused the resistance?
 Why is the pesticide called a “selecting agent”?
 What do the most fit roaches do?
 What is this an example of?
 What does the bug clipart in the corner represent?