DNA (Gene) Mutations

What is a gene mutation? Parts of DNA will have a base (or more) missing, added, or incorrect A mistake in the genetic code Wrong instructions  wrong building materials  wrong structure.

How common are mutations? Mutations occurs at a frequency of about 1 in every 1 billion base pairs Everybody has about 6 mutations in each cell in their body! A fun fact about how common mutations are. Explain that everyone has mutations, although they are not always seen because the mutation may have occurred in a section of DNA that doesn’t make a protein.

If I have that many mutations, why don’t I look weird? Mutations are not always seen. Every part of your DNA doesn’t make a protein or trait. Remember introns and exons? Some genes are recessive and are therefore hidden, they can be passed to your kids but you don’t notice them. Explain that everyone has mutations, although they are not always seen because the mutation may have occurred in a section of DNA that doesn’t make a protein or the mutation may cause a cell to die (while not affecting the function of the organ).

The most common types of gene mutations are: Substitution Point mutations Frame shift mutations (2 kinds) Insertion Deletion General information about the three most common types of mutations to transition into the examples

DNA (Gene) Mutation What happened? Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TGC - TTC Ask students if they can figure out what is happening in this mutation. Answer is on the next slide. What happened?

DNA (Gene) Mutation #1 *Adenine was accidentally replaced with thymine Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TGC - TTC See if students can figure out what the name of this mutation would be; answer is on the next slide. *Adenine was accidentally replaced with thymine *What is this mutation called?

Substitution (point mutation) Normal DNA: CGA – TGC – ATC Amino acids: Ala -- Thr -- stop Mutated DNA: CGA – TGC – TTC Amino acids: Ala -- Thr -- Lys Explain and emphasize how this type of mutation will only affect one amino acid What will happen to the amino acids? How many will be affected?

DNA (Gene) Mutation #2 What happened? Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TAG – CAT - C Ask students if they can figure out what is happening in this mutation. Answer is on the next slide. What happened?

DNA (Gene) Mutations Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TAG – CAT - C *Adenine was inserted,causing the remaining DNA to shift to the right *What is this mutation called? See if students can figure out what the name of this mutation would be; answer is on the next slide.

Insertion Normal DNA: CGA – TGC – ATC Amino acids: Ala -- Thr -- stop Mutated DNA: CGA – TAG – CAT – C Amino acids: Ala -- Tyr -- Val -- ….. Also, explain and emphasize how this type of mutation will affect all the amino acids after the mutation What will happen to the amino acids? How many will be affected?

DNA (Gene) Mutation #3 What happened? Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TCA- TC Ask students if they can figure out what is happening in this mutation. Answer is on the next slide. What happened?

DNA (Gene) Mutation Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TCA- TC See if students can figure out what the name of this mutation would be; answer is on the next slide. *Guanine was removed, causing the remaining DNA to shift to the left *What is this mutation called?

Deletion Normal DNA: CGA – TGC – ATC Amino acids: Ala -- Thr -- Stop Mutated DNA: CGA – TCA- TC Amino acids: Ala -- Ser --……. Explain and emphasize how this type of mutation will affect all the amino acids after the mutation What will happen to the amino acids? How many will be affected?

Mutagen? What’s that? • What causes mutations? Replication errors Transcription errors Cell division errors Spontaneous changes Mutagens Mutagen? What’s that? “Stuff” that causes mutations when a cell is exposed. Examples: UV light, Xrays, chemicals, etc. Explain that many mutations occur naturally (when your DNA replicates before cell division). Many mutations are caused by mutagens (UV light, exposure to chemicals, radiation, etc.) What happens? Most of the time the mutation is harmless because there are sections of DNA that do not code for protein (junk DNA) but sometimes the mutations can cause disorders such as Huntington’s disease and sickle cell anemia.

What happens to someone with a mutation? That all depends….. What kind of mutation it is. How many proteins are affected. Where in the polypeptide chain is the mutation. How many cells does it affect. Mutations can be fatal, harmful, beneficial or nuetral.

have the least effect on an • Which mutation would organism? have the least effect on an On intron sections of DNA On unexpressed recessive traits. Point mutations/substitutions Only affects 1 amino acid. Least Effect? A mutation on an unexpressed recessive trait or substitution because it only affects ONE amino acid; insertion and deletion affect ALL the amino acids after the mutation. Most Effect? Mutations in egg and sperm cells can cause problems in the baby whereas mutations in body cells can only cause problems for that person (not his/her offspring).

have the most effect on an • Which mutation would organism? have the most effect on an Frame-shift mutations: Deletions and insertions affect all amino acids after the mutation.

• When would a mutation have the most effect on an organism? During Meiosis If gametes are produced with mutations, those mutations will be passed onto the offspring……. Every cell of organism will contain mutation.

Repairing DNA Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides. The greater the exposure to a mutagen such as UV light, the greater the chance that a mistake will not be corrected.