Evolution: Online Course for Teachers: Session 4- Explore Part D

	SESSION 4

	Engage

	Explore

	Part A:	Natural Selection

	Part B:	Adaptations

	Part C:	Genetic Variation By Mutation

	Part D:	Genetic Variation By Recombination

	Part E:	Nonselective Mechanisms

	Explain

	Elaborate

	Evaluate


	Resources

	Facilitator Notes

SESSION 4: What Are the Processes for Evolution?

Explore Part D: Genetic Variation By Recombination

Recombination is usually the most immediate cause of variability.
Recombination can occur in at least three ways:


	1.	Crossing over of chromosomes during meiosis

	2.	Random assortment of maternal and paternal chromosomes during the production of egg and sperm

	3.	Random combination of egg and sperm at fertilization.



		For further information on recombination see the Palomar College Web site.

		For over 25 years Robert Vrijenhoek has studied unique populations of minnows in the small hillside pools of the Sonoran desert in Mexico. Here he found two different species of minnows living side-by-side, one an asexual reproducer and the other a sexual reproducer. Vrijenhoek has been trying to understand which conditions might favor the sexual minnows and which favor the asexual ones. To find out what he discovered about the value of sexual reproduction, view the Evolution Show Five video segment "Red Queen."

Red Queen View in: QuickTime \| RealPlayer

Describe the advantages of sexual reproduction for the minnow populations.



		Read "The Advantages of Sex" Web essay.


	Teaching Evolution Home \| Technical Requirements \| Visit the Evolution Web site at PBS Online

	© 2001 WGBH Educational Foundation and Clear Blue Sky Productions, Inc. All rights reserved.