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?