Name:______________________Date:__________Period:____
Biochemical Evidence for Evolution
3.4.2.3.
Evolution is the theory that species change over time. There is evidence
that show evolutionary relationships. Biologists use fossils of organisms that lived
in the past, but they also use evidence in the organisms that are alive today. By
comparing the DNA and amino acids of organisms alive today biologists can
determine which organisms are more closely related to each other. We cannot see
DNA or proteins, but we can use a technique called gel electrophoresis to help
compare them. Scientists can use either DNA or amino acids in gel
electrophoresis. Gel electrophoresis is the most accurate way of determining
the relation between organisms.
REMEMBER THIS!!!
Gel electrophoresis is the process where the DNA of an organism can be
compared to the DNA of another organism to determine if they are similar.
The results of the gel electrophoresis determine if certain organisms are
related. If the DNA patterns match, then they are closely related. If the gel
electrophoresis shows that the DNA bands do not match, then they are not closely
related. By examining the results, the degree of kinship of organisms can be
determined.
Question 1. Why would matching the DNA of different animals determine if they
are related?
Gel electrophoresis is a technique that uses electricity to pull on the
negative charge in DNA or amino acid molecules. The electricity pulls on DNA or
amino acids that have been cut into pieces with special enzymes. They are then
pulled through a gel so that the small pieces can move faster than the longer
pieces. Since smaller pieces move faster than larger ones, the DNA or amino acids
are spread out all over the gel. When the process is stopped, the spread of DNA
or amino acids creates a characteristic pattern on the gel. This pattern is unique
for every individual. By comparing the patterns, scientists can determine if the
organisms are similar.
REMEMBER THIS!!!
Gel electrophoresis creates a pattern in the gel that is unique to every
individual.
Question 2. Why are the patterns created by gel electrophoresis useful?
Biologists use gel electrophoresis to compare the DNA or amino acids of
different organisms. If the DNA or amino acids are similar the pattern will
look similar. If the patterns are similar, then they organisms are closely related.
If they are not similar, then they are not closely related. For example, if some
DNA of a horse, a rabbit, and a snake were cut into pieces and run through gel
electrophoresis, the banding pattern at the end of the process might look like
this.
______________________________________________________________
-
end
+
end
Horse Well
Rabbit Well
Snake Well
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The well is where the cut pieces of DNA where placed. When the electricity
was turned on, they moved toward the positively charged end of the gel.
Examine the example. The number of similar segments suggests that horses and
rabbits have DNA that is more similar than horses and snakes or rabbits and
snakes.
REMEMBER THIS!!!
The more bands that two organisms have in common on a gel, the more similar
their DNA. The more similar the DNA of two organisms, the more closely they
are related.
Question 3. How would the gel electrophoresis pattern of a mother and child
compare?
Question 4. What would the gel electrophoresis pattern look like if you submitted
two samples from yourself and compared them?
TEST YOURSELF
Fill in the Blank
well
evolution
gel electrophoresis
banding pattern
small pieces
DNA
negative
related
long pieces
proteins
electricity
bands
1. ____________________________________ is the theory that species
change over time.
2. There is evidence for evolution in the _________ and ________________ of
organisms that are alive today.
3. Since we cannot see DNA or proteins, a technique called
____________________ is used to compare them.
4. The DNA or protein is cut into pieces with special enzymes and then placed into
a ________.
5. There is a ___________________ charge on DNA that is attracted to a
positive charge at the other end of the gel.
6. The ________________________ pulls the pieces of DNA or protein away
from the well.
7. The ________________________ of DNA move faster through the gel than
the ________________.
8. This creates a _____________________________ in the gel after the
electricity is turned off.
9. By comparing the location of the bands, similarities in DNA can be seen. The
more ____________________ two organisms have in common, the more
similar their DNA is.
10. The more similar the DNA is between two organisms, the more closely
_________________ they are.
Answer the Following
1. What procedure must biologists use to be able to compare the DNA or amino
acids of different organisms?
2. What force pulls the pieces of DNA or proteins through an electrophoresis gel?
3. Which travels faster, the small sample pieces or the large pieces?
4. When the bands in the banding pattern are compared, what is assumed when
there are many similar bands between different organisms?
5. When there are many similar bands, what is assumed about the DNA of the
organisms being compared?
6. Which do you predict would appear more similar in a gel electrophoresis
pattern, a cat and a lion, or a cat and a clam? Explain your answer.
7. Explain how the gel electrophoresis patterns are used to establish a
relationship between organisms.