Chapter 13 Notes

Mutations

 

What is a mutation?

Heritable changes in the genetic information (DNA).

 

What causes mutations?

Mutagens such as chemicals, UV radiation and viruses.

 

Mutations can occur in two different types of cells:

 

1. Somatic (body) cells

2. Gamete (sex) cells

 

Mutations that occur in somatic (body) cells usually result in killing that body cell only.

 

An exception to this is if the mutation occurs to the DNA that controls regulation of the cell cycle. This can result in cancer.

      Somatic mutations usually do not affect the individual.

      Somatic mutations can NOT be passed on to the next generation.

 

Mutations that occur in gamete (sex) cells means that every cell of the developing fetus/baby will have that mutation.

      Gamete mutations usually do affect the individual with some genetic disorder.

 

      Gamete mutations can be passed on to the next generation.

 

There are two types of mutations that can occur in gamete cells:

 

1. Gene Mutations

2. Chromosomal Mutations

 

 

2 types of Single Gene Mutations:

1.                      Point Mutation: a single point in the DNA sequence is affected.

 

      Can be a substitution in which one base is changed into another base.

 

 

Point mutations usually affect no more than a single amino acid. The protein may be slightly affected or not affected at all.

 

 

 

2. Frameshift Mutation: a single gene or nitrogen base is deleted or added from the mRNA sequence causing a shift in the “reading frame” of the genetic message.

      Can be an insertion in which one base is inserted in the DNA sequence.

      Can be a deletion in which one base is deleted in the DNA sequence.

 

 

The effect of frameshift mutations is usually more dramatic. Frameshift mutations may change every amino acid that follows the point of the mutation. Frameshift mutations can alter a protein so much that it is unable to perform its normal functions.