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Online Course for Teachers: Teaching Evolution

About this Course 


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:


Crossing over of chromosomes during meiosis


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


Random combination of egg and sperm at fertilization.

Taking it further

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

Image of Robert Vrijenhoek working in the field.

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.


Taking it further

Read "The Advantages of Sex" Web essay.

Next: Explore Part E: Nonselective Mechanisms

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