Mutations MUTATION A change in the nucleotide sequence

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?

• Mutations happen regularly • Almost all mutations are neutral • Chemicals & UV radiation cause mutations • Many mutations are repaired by enzymes 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

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

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

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

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

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

• 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

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

Chromosome Mutation Animation

• 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

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

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

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

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

• 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 3 rd generation child Y marries a normal male, what is the probability that they will have 2 child carriers?