1. Mutations
Read the lesson title aloud to students.

2. Learning Objectives
Define mutations and describe the different types of mutations.
Describe the effects mutations can have on genes.
Click to show each of the learning objectives.
Play the game of “pass the message.”
Start by whispering a message to a person on one side of the room. The message should be a complex sentence or two sentences and it should include some significant details.
Ask the student to whisper the message to the student closest to him or her.
That student should then pass the message on to the next person, and so on, until the message makes it to the other side of the room.
When the message gets to the other side of the room, have the last person say the message out loud and compare what is said to the message that was originally given.
Relate what happens to the message in this game to how mistakes are introduced in genes as they are copied and passed on to offspring.
Ask: Do you know what mistakes in genes are called?
Answer: mutations
Tell students that at the end of this lesson, they will be able to describe the different types of mutations and the effects that mutations can have on genes.

3. Mutations Mutations are heritable changes in genetic information.
Ask: What are mutations?
Answer: Mutations are heritable changes in genetic information.
Click to reveal this answer.
Point out that the enlarged shape of the flower shown is caused by a mutation that affects the growing regions of the flower tissue.

4. Types of Mutations Mutations fall into two basic categories:
Gene mutations
Chromosomal mutations
Tell students: Mutations come in many different forms. The flower shown on the previous slide and the lion shown on this one are just two of countless examples.
Explain to them that all mutations fall into two basic categories.
Click to reveal each category.
Point out that a genetic condition called leucism leaves the lion shown without pigments in its hair, skin, and eyes.
Ask: Which type of mutation is likely to be more harmful?
Answer: A chromosomal mutation is likely to be more harmful because many genes are found on one chromosome.

5. Gene Mutations: Point Mutations
A point mutation is a change in a single nucleotide.
There are three types of point mutations:
Tell students: Changes in a single nucleotide can affect the amino acid sequence of proteins.
Point mutations include three types: substitutions, insertions, and deletions.
Click to highlight these types.
Tell students: You will learn more about each mutation in the coming slides.
Point mutations generally occur during replication.
If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.
Ask: What can a mutation do to the outcome of transcription and translation?
Answer: Mutations change the code. This changes the mRNA code. This changes the amino acids in the protein. This changes the protein structure. This can affect the protein function.

6. Point Mutations: Substitutions
In a substitution, one base is changed to a different base.
Explain to students that substitutions usually affect no more than a single amino acid, and sometimes they have no effect at all.
Ask: In the example shown, before the mutation, what is the second codon and what amino acid does it specify?
Answer: The second codon is CGU and it specifies arginine.
Click to highlight the arginine information.
Point out that when a single nucleotide is replaced, in this case thymine replacing cytosine, the codon is changed.
Ask: In the example shown, what change occurred in the codon?
Answer: The second codon is now CAU, which specifies histidine.
Click to highlight the histidine information.
Point out to students that not all mutations result in a change to the amino acid.
For example, if a mutation changed one codon of mRNA from CCC to CCA, the codon would still specify the amino acid proline.
Ask a volunteer to point out CCC and Proline.
Click to highlight the CCC.
Then ask the same volunteer to point out why CCA would result in the same amino acid.

7. Point Mutations: Insertions and Deletions
Insertion mutation: when a single extra base is added into the code
Deletion mutation: when a single base is removed from the code
Point out to students that the significance of either insertions or deletions can be dramatic.
Ask: Why do you think that an insertion or a deletion could have a dramatic effect?
Answer: Because the genetic code is read three bases at a time. If a nucleotide is added or deleted, the entire reading frame is shifted. Consequently, every amino acid after the mutation will likely be altered.
Tell students: Insertions and deletions are also called frameshift mutations for this reason.
These mutations can alter a protein so much that it is unable to perform its normal functions.
Activity: Write the following sentence on the board without spaces: Theboysawthetandogrun.
Tell students: Read the sentence three letters at a time.
Add an “x” after the first “The” and give the students the same directions to read the sentence.
Discuss how this example relates to frameshift mutations.

8. Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation
Tell students: Sometimes a mutation affects an entire chromosome. Chromosomal mutations can change the location of genes on chromosomes and can even change the number of copies of some genes. There are four types of chromosomal mutations.
Briefly explain the diagram and how each section of the chromosome consists of many genes.
Tell students: Deletion involves the loss of all or part of a chromosome.
Click to highlight deletion.
Duplication produces an extra copy of all or part of a chromosome
Click to highlight duplication.
Inversion reverses the direction of parts of a chromosome.
Click to highlight inversion.
Translocation occurs when part of one chromosome breaks off and attaches to another.
Click to highlight translocation.
Ask: What is the difference between inversion and translocation?
Answer: An inversion mutation reverses the direction of part of one chromosome. A translocation mutation attaches part of one chromosome to another chromosome.

9. Effects of Mutations
Mutations can harm, help, or have no effect on an organism.
Some mutations arise from mutagens—chemical or physical agents in the environment.
Explain how the effects of mutations can be minimal, beneficial, or disastrous to an organism.
Explain to students that chemical mutagens include certain pesticides, a few natural plant alkaloids, tobacco smoke, and environmental pollutants.
Physical mutagens include some forms of electromagnetic radiation, such as X-rays and ultraviolet light.
Tell students: If these agents interact with DNA, they can produce mutations at high rates.
Cells can sometimes repair the damage, but when they cannot, the DNA base sequence changes permanently.
Ask: What would be the effect of a compound that interferes with base pairing?
Answer: It would increase the error rate of DNA replication.
Point out that other compounds can actually weaken the DNA strand, causing breaks and inversions that produce chromosomal mutations.

10. Effects of Mutations: Harmful
Some of the most harmful mutations are those that dramatically change protein structure or gene activity.
Example: Sickle cell disease affects the shape of red blood cells.
Tell students: Some of the most harmful mutations are those that dramatically change protein structure or gene activity.
The defective proteins produced by these mutations can disrupt normal biological activities and result in genetic disorders.
Some cancers, for example, are the product of mutations that cause the uncontrolled growth of cells.
Point out that sickle cell disease is a disorder associated with changes in the shape of red blood cells, as shown in this image.
Sickle cells are crescent- and star-shaped.
Click to highlight a normal red blood cell versus a sickle cell.
Explain that this disease is caused by a substitution mutation in one of the polypeptides found in hemoglobin, the blood’s principal oxygen-carrying protein. Among the symptoms of the disease are anemia, severe pain, frequent infections, and stunted growth.
Sickle cell
Normal red blood cell

11. Effects of Mutations: Beneficial
Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments.
Explain that some of the variation produced by mutations can be highly advantageous to an organism or species.
Tell students: Mutations have helped many insects become resistant to chemical pesticides and have enabled microorganisms to adapt to new chemicals in the environment.
Also explain that plant and animal breeders often make use of “good” mutations. For example, when a complete set of chromosomes fails to separate during meiosis, the gametes that result may produce triploid (3N) or tetraploid (4N) organisms. The condition in which an organism has extra sets of chromosomes is called polyploidy.
Ask: Based on this information, why might plant breeders want to encourage these “good” mutations?
Answer: Changes to the ploidy number of citrus plants can affect the size and strength of the trees as well as the quality and seediness of their fruit. Polyploid plants are often larger and stronger than diploid plants. Important crop plants—including bananas and limes—have been produced this way.