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Life 101
What drives evolution?
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Mutations
Definition: A change in the DNA. Remember, DNA is the code of life. It determines what traits will be
expressed and what traits won’t be expressed. A single change in the sequence of DNA is a mutation.
A mutation can be neutral, positive or negative for an organism. A negative mutation means it is harmful for the
organism. There are many genetic diseases that are caused by mutations ex. Down’s Syndrome, Parkinson’s
Disease.
Effects on Evolution: Some mutations are positive, however, give the organism an advantage in life and may be
selected for. If this gene is then passed on hereditarily, over time, a new species may arise.
Ex. Antibiotic resistant bacteria. These bacteria have a change in their genetic code that makes them invulnerable
to antibiotics. This is a positive mutation for the bacteria.
Questions:
1. How can mutations lead to differences in gene frequency?
2. How do mutations cause evolutionary change?
3. Can you think of another positive mutation?
4. Create a short skit on how mutation drives evolution.
Gene Flow or Migration
Definition: The rate of the “movement” or flow of an organism within a group of organisms and between different
groups. The immigration and emigration of organisms and its genes.
Gene Flow depends on the organism. Corn, for example, have a low rate of gene flow because it is stationary and
is wind pollintated, so the genes can only “move” 50 feet or so. Insects can have a high rate of gene flow because
of their ability to move around.
Effects on Evolution: It can re introduce genes within a group of organisms and increase the differences in genes.
It can also decrease the differences of genes between two groups. If gene flow stops between two groups of
organisms, and the groups become different enough, new species may arise.
Questions:
1. How can gene flow lead to differences in gene frequency?
2. How does gene flow cause evolutionary change?
3. Draw a diagram that represents gene flow.
Genetic Drift (Textbook pg 400)
Definition: It is the random change in the amount/ concentration of a particular gene in a group of organisms. It
takes place in all populations but its effect is better seen in small populations.
Effects on Evolution: Just by chance, some genes can be more or less common. For example, some individual
may have more descendants than another and thus have more of their genes passed on. Over time, if these chance
occurances keep happening, these genes may spread throughout the entire group of populations. In effect, it’s like
flipping a coin with genes.
Gene frequency: The number of times a gene is seen in a population.
Questions:
1. How does genetic drift lead to differences in gene frequency?
2. How do differences in gene frequency lead to evolution?
3. Create a short skit that explains genetic drift.
Non Random Mating
Definition: When individuals selectively choose a mate based on their traits. Ex. Male lions are “chosen” on their
size and strength. Ex. Weaver birds are chosen on their ability to make a nest.
Effects on Evolution: If you get a mate, you pass your genes on. If you are chosen due to a specific trait, those
traits will be passed on to the next generation.
Questions:
1. How does non-random mating create an imbalance in an amount of specific genes?
2. Think of another example of non random mating.
3. Create a short skit explaining non random mating.