1. Genetics and Evolution: Hey, Aren’t Those Chapters in Different Parts of the Book?
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This lesson will explore the relationship between evolution and genetics. It should be used after both topics have been covered (at least preliminarily).
PowerPoint presentation and accompanying activity by Alison Cawood.

2. Just to review… In general terms:
Genetics is the science of heredity. It explains how traits are passed from parents to offspring.
Evolution is the study of the historical progression of a related group of organisms.
Just to review vocabulary and make sure that everyone is using the same terms.

3. Evolution works through the process of natural selection.
Natural selection is the process through which the traits that are most likely to help an organism survive and reproduce become more common in a given population.
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Here it could be useful to ask students if they can think of any examples of natural selection.

4. Examples of Natural Selection include:
Antibiotic resistance in bacteria
Pepper moths in England during the Industrial Revolution
Galapagos Finches
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Bacteria that are not killed by antibiotics will be able to survive and produce more offspring. Because they are able to produce more offspring than bacteria that are killed or weakened by antibiotics, the next generation of bacteria will contain more of the offspring from antibiotic resistant bacteria than from non-antibiotic bacteria.
Before the industrial revolution, pepper moths were primarily light colored, and dark moths were rare in nature. After the industrial revolution, there was more ash, soot, and smoke in the air, and it became easier for birds to prey on the light colored moths. Soon, light colored moths became rare and the dark colored moths were the most commonly found in nature. In non-industrial areas, the white moths stayed more common with dark moths still rare.
The Galapagos Islands are a chain of islands in the Pacific Ocean. Each island has different plants and animals that live there. There are finches found on most of those islands. The finches look very similar. The only visible difference between them is their beaks. Some have beaks that are better for cracking seeds while others have beaks that are better for getting insects out of the ground. The beaks correspond to the most abundant type of food on a given island. Islands with lots of available insects have finches with beaks that are really effective at eating the bugs.

5. So, what does all of this have to do with genetics?
In order for natural selection to work, there has to be something to select from!
These choices are created by the genetic variability that exists in populations.
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Sexual reproduction and the ability to pass traits from one generation to the next are what allows natural selection to work. If there was no variability, there can be no selection because there is nothing to select from.

6. The other important factor of natural selection is environmental change.
If there is no environmental change, no one trait is selected over another because there nothing that makes one trait an advantage over another one.
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In order for one trait to become better than another one, there has to be a reason. For example, in humans, there is no advantage or disadvantage to having brown eyes over having blue eyes. Brown eyes are more common because they are the dominant allele, but there is no natural selection for them. If the environment changed so that brown eyes were a disadvantage, blue eyes would become much more common.

7. So, natural selection works by…
1. Having variation in heritable traits.
2. Environmental change leads to selection of some traits over others X X X X X X
3. Parents with advantageous traits pass them to offspring.
4. The more advantageous traits become the most common.
If there is no variation, there can be no natural selection. That is why sexual reproduction is such a good strategy. It leads to increased genetic diversity by randomly combining the alleles of the parents. Every generation creates new combinations of alleles.
If there is no change in the environment or no some reason that one trait is more advantageous than another, there will be no pressure to remove that allele from the population. It will follow normal inheritance proportions (like those determined by the Hardy-Weinberg equilibrium principle) based on the dominance/recessive pattern for the alleles leading to that trait.
The traits that are selected for will give the individuals that display those traits advantages in the form of increased survivorship and increased production of offspring. In other words, the individuals who have the “good” traits will survive to pass those traits along to their offspring. The ones with the “bad” traits won’t be able to pass their genes (traits) on as effectively.
Eventually, unless the environment changes in a different way, the “bad” traits will become increasingly rare, and may disappear completely. The good traits will become more and more common.

8. Eventually…
The population may change such that there are no alleles left for the non-advantageous traits. They can disappear from the population completely. X X
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Through enough generations, you can lose not only the physical trait, but any genetic traces of it.

9. This can lead to speciation
Imagine there is a storm that blows 1,000,000 of our bug to one island and 1,000,000 to another island.
Speciation is the creation of a new species (one that has never existed before).
Island 1 represents an environmental change. Island 2 represents the same environment.
Island 1 has lots of food, but most of it is high up in trees.
Island 2 is very similar to the island the bugs came from.

10. After many generations
Island 2
Island 1
Because the food is located in the trees, the bugs that are better climbers are going to be more fit so they will be able to have more offspring. This becomes more and more refined until the bugs on island 1 are great climbers. The have changed sufficiently that they would no longer be able to breed successfully with the bugs from island 2 or from their original island.
It is important to remember that the change in environment did not cause the change in the bugs. The variation had to exist before the environment changed in order for it to appear in the island 1 bugs. However, because the advantage was so great, the animals with longer than average legs had lots more offspring. These traits were selected by the environment, not created by it.
Bugs from Island 2 remained very similar to their ancestors who settled on the island after the storm.
Bugs from Island 1 developed long legs and hooked feet do that they can easily climb trees to get to food.

11. Where does the variation come from?
The genetic variation comes from random mutations in the genes.
The mutations occur when DNA replicates.
Insertions
Deletions
Frame Shifts
Inversions
Point Mutations
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The mutations occur naturally. They can happen just because mistakes happen whenever something is done millions of times. It can also happen as a result of environmental factors (like UV radiation causing skin cancer).
Insertions: Extra segments of DNA are inserted (can be one base or many bases) is inserted incorrectly into a DNA strand.
Example: The cat ate the mat.
Insertion: The cat ate the rat mat.
Deletion: Segments of the DNA (one base or many bases) are deleted from the DNA strand.
Deletion: The cat the mat.
Frame Shifts: Pieces of DNA that aren’t in multiples of 3 are inserted or deleted into the strand. DNA is read in sets of 3 (called codons). For example, deleting 1 base will change the way that all the following sets of 3 are read.
Example: The cat ate the mat.
Frame Shift: The ata tet hem at
Inversions: A section of DNA is reversed.
Inversion: The cat eht eta mat.
Point Mutations: Point mutations occur when only one base is changed. This can cause problems (by changing the amino acid that a codon codes for) or not depending on where the change occurs and what the change is.
Point Mutation: The cat tte the mat.

12. In summary, DNA mutations create new alleles
Alleles are recombined through sexual reproduction producing new traits
As environments change, different traits may become dangers or advantages
The parents with advantageous traits are more fit so they have more offspring (some of which will have the advantageous trait)
Though many generations, the advantageous traits will become more and more common in the population