Mutations

MUTATION = A change in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring What Are Mutations?

Are Mutations Helpful or Harmful? Mutations happen regularly Almost all mutations are neutral Chemicals & UV radiation cause mutations Many mutations are repaired by enzymes Are Mutations Helpful or Harmful?

Are Mutations Helpful or Harmful? Some type of skin cancers and leukemia result from somatic mutations Some mutations may improve an organism’s survival (beneficial) Are Mutations Helpful or Harmful?

So…Are Mutations Helpful or Harmful?

Types of Mutations

Chromosome Mutations May Involve: Changing the structure of a chromosome The loss or gain of part of a chromosome Chromosome Mutations

Chromosome Mutations Five types exist: Deletion Inversion Translocation Nondisjunction Duplication Chromosome Mutations

1. Deletion Due to breakage A piece of a chromosome is lost A B C D E F G H A B C G H 1. Deletion

2. Inversion Chromosome segment breaks off A B C D E F G H Chromosome segment breaks off Segment flips around backwards Segment reattaches A B C F E D G H 2. Inversion

3. Translocation Involves two chromosomes that aren’t homologous A B C D E F G H I J K L M N O P A B C D E F G H I J Involves two chromosomes that aren’t homologous Part of one chromosome is transferred to another chromosome K L M N O P 3. Translocation

4. Nondisjunction Failure of chromosomes to separate during meiosis Causes gamete to have too many or too few chromosomes Example : Down Syndrome (Trisomy 21) – caused by ___ copies of chromosome 21 4. Nondisjunction

5. Duplication Occurs when a gene sequence is repeated A B C D E F G H A B C D C D E F G H Occurs when a gene sequence is repeated 5. Duplication

Chromosome Mutation Animation

Gene Mutations Change in the nucleotide sequence of a gene May only involve a single nucleotide May be due to copying errors, chemicals, viruses, etc. Gene Mutations

Types of Gene Mutations Include: Point Mutations Substitutions Frameshift Insertion Deletion Types of Gene Mutations

1. Point Mutation Change of a single nucleotide Usually includes the substitution of ONE nucleotide in a gene 1. Point Mutation

Point Mutation (substitution) Original: The fat cat ate the wee rat. Point Mutation (“a” subs for “t”): The fat caa ate the wee rat. Point Mutation (substitution)

Point Mutation (substitution) The fat caa ate the wee rat. Is the sentence still understandable? Would a point mutation likely cause big problems? What do the simple, three-letter words above represent? Point Mutation (substitution)

Sickle Cell disease is the result of one base substitution Occurs in the hemoglobin gene Point Mutation

Frameshift Mutation Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Can cause proteins to be built incorrectly Frameshift Mutation

Frameshift Mutation Original: The fat cat ate the wee rat. Frame Shift (“a” added): The fat caa tat eth ewe era t. Frameshift Mutation

Amino Acid Sequence Changed

Cystic Fibrosis is the result of a frameshift mutation 2 frameshifts in the CFTR gene: 2-base insertion 1 base deletion Frameshift Mutation

Gene Mutation Animation

Does it still make sense? If a gene mutation does not change the amino acid, it’s called a SILENT mutation. If a gene mutation changes the amino acid, it’s called a MISSENSE mutation. If a gene mutation changes the amino acid to a “stop” codon, it’s called a NONSENSE mutation. Does it still make sense?

End notes…

What is the probability of child V being affected? What is the chance that child V will be a carrier for the disease? If 3rd generation child Y marries a normal male, what is the probability that they will have 2 child carriers?