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!

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.

The most common types of gene mutations are : Substitution Point mutations Frame shift mutations (2 kinds) Insertion Deletion

DNA (Gene) Mutation Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TGC - TTC What happened?

DNA (Gene) Mutation #1 Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TGC - TTC *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 What will happen to the amino acids? How many will be affected?

DNA (Gene) Mutation #2 Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TAG – CAT - C 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?

Insertion Normal DNA: CGA – TGC – ATC Amino acids: Ala -- Thr -- stop Mutated DNA: CGA – TAG – CAT – C Amino acids: Ala -- Tyr -- Val -- ….. What will happen to the amino acids? How many will be affected?

DNA (Gene) Mutation #3 Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TCA- TC What happened?

DNA (Gene) Mutation Normal DNA: CGA – TGC – ATC Mutated DNA: CGA – TCA- TC *Guanine was removed, causing the remaining DNA to shift to the left *What is this mutation called?

Normal DNA: CGA – TGC – ATC Amino acids: Ala -- Thr -- Stop Mutated DNA: CGA – TCA- TC Amino acids: Ala -- Ser --……. Deletion What will happen to the amino acids? How many will be affected?

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.

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.

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.

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 an organism? have the most effect on 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.

Chromosomal mutations Mutations that involve changes in number or structure of chromosomes.

Insertion/duplication When part of a chromatid breaks off and attaches to its sister chromatid, an insertion occurs. Duplication is when an extra copy of a gene is made. A B C D E- F G HA B C B C D E- F G H

Deletion When a part of a chromosome is left out, a deletion occurs A B C E- F G H A B C D E - F G H deletion

Inversion When part of a chromosome breaks off and reattaches backwards, an inversion occurs. Inversion A B C D E- F G HA D C B E- F G H

Translocation When part of one chromosome breaks off and is added to a non-homologous chromosome, a translocation occurs Translocation A B C D E- F G H W X A B C D E- F G H W X Y - ZY - Z

Nondisjunction Failure of chromosomes to separate properly. This results in too many chromosomes or too few.

Trisomy 21: three copies of chromosome number 21  “Down syndrome. Turner’s syndrome: Female with only one copy of the X chromosome. Klinefelter’s syndrome: Male with an extra X chromosome.