Download GENETIC VARIATION The raw material of biological evolution

GENETIC VARIATION
The raw material of biological evolution
Populations of organisms vary in heritable characteristics. Since the mechanisms
of biological evolution act upon this variation, without it, there would be/would
have been no biological evolution, and life on earth would be quite different. A
simple inventory of traits of an easily obtained group of organisms (or humans)
can introduce students to this concept.
Materials
• Representatives of a population of organisms; for example, snails, coleus, other insects
or plants; several per group
• Measuring tools – rulers, tape measures, scales, etc.
• Magnifying glasses
• Paper/pencils for recording data
• Optional, and for snails only: Materials to test behaviors, such as water bottles for
spraying, different foods to test preferences, stop watches to test speed of locomotion,
etc.
To Do and Notice
The following example is for conducting the experiment with snails, but can easily be
modified to any population of organisms
Introduce the snails to a contained area and observe them. Do they all appear
identical? How do they differ? Have a discussion of these differences with the
entire class. As a class, choose at least four different anatomical or behavioral
traits, and devise a way to measure or assess the variation of each trait between
individuals. Record your answers. Some possible traits may be:
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Length of foot
Length of antennae when extended
Color or pattern of shell
Food preference
“Fear” or “curiosity”
Speed of retreat
Height of shell
Combine all the data of the class, and look for patterns. Of the four traits, are any
variants more predominant in the population? Can you think of how some trait
variants could be advantageous to an individual?
What’s Going On?
Should environmental conditions change (anything from climate to food type and
availability) natural selection will favor those individuals whose genetic variations
endowed them with a phenotype that allows them to survive and reproduce thereby
passing on this genetically inherited trait. Over time, the genes for this trait (alleles) will
become more predominant in the population as other less “fit” individuals die off and no
Karen E. Kalumuck
Exploratorium Teacher Institute
Copyright 2006 DRAFT
longer pass their genes to succeeding generations. With the passage of much time and
perhaps with other mechanisms in play, a new species (or new species) may emerge from
the original population.
Without genetic variation and the associated phenotypic variants, should conditions
change, (and conditions are always changing) a population would have no individuals
who could survive and pass along their genes to succeeding generations. The population
would become extinct.
Karen E. Kalumuck
Exploratorium Teacher Institute
Copyright 2006 DRAFT