1. The concepts covered here can be reviewed in your textbook, pages 223-225, and your lecture notes.

2. Review the terminology involved in classifying mutations. On a piece of paper write down the definitions of the following terms:

Mutation
Base substitution
Insertion
Deletion
Spontaneous mutation
Wild type
Reverse mutation
Frameshift mutation

3. On a piece of paper, copy and classify the following mutations as substitution, insertion, deletion, or frameshift. After you are done, check your answer by mousing over the word ANSWER below. If some of your answers are wrong, try to figure out why? Remember that many (but not all) insertions and deletions are also frameshift mutations. What has to be true for an insertion/deletion to be also a frameshift?

ANSWER

4. Depending on where the mutation occurs, a base substitution can be result in three types of mutations. On a piece of paper, write down the definitions of silent, missense, and nonsense mutation. Then, copy the mutations below and for each one write (a) the mRNA, (2) the protein that will be made, and (3) the type of mutation it is (silent, missense, nonsense). Use your textbook to get the genetic code. Make sure when you are writing the mRNA to transcribe the template DNA strand, and pay attention to the directions! Make sure that when you translate the mRNA, you are going 5' to 3'.

ANSWER (ONLY SHOWS EXAMPLE 1)

5. How are mutations introduced in DNA? There are two ways for that to happen - mutagens (next subunit) or mistakes during replication. Mistakes during replication can be introduced in a variety of ways. One way for that to happen is for DNA polymerase to make a mistake. Researchers have studied DNA polymerase and have found that it is subject to two types of selection that seemingly contradict each other. On the one hand there is selection to keep the polymerase good at proof-reading (fixing mistakes). On the other hand, there is selection for the polymerase to be able to introduce some mistakes in DNA (so a perfect polymerase that is able to fix all mistakes would be selected against). Can you try to explain why the polymerase might be under those two types of selection?

6. If you feel that you have mastered the concepts on this page, you can move to the next topic of this sub-unit, which explores mutagenesis and DNA repair.