MUTATIONSChanges in genotype can result in changes in phenotype.

Mutations are Changes to DNAChanges in DNA sequences can affect the phenotypes of organisms by affecting protein structure and gene expression.

Causes of MutationsMutagens: Substances that cause mutations by interacting with DNA.

DNA Replication Mistakes: ~1/1,000,000,000 bases replicated in humans.

Mutations can be positive, negative, or neutral, depending on where they occur.

Point Mutations

• One DNA base is replaced by another DNA base.

• Substitution

Sickle Cell Anemia is due to a point mutation.

Point Mutations

Silent:The substitution changes a codon to another codon for the same amino acid.

Point Mutations

Missense:The substitution changes a codon to a codon for a different amino acid.

Point Mutations

Nonsense:The substitution changes a codon to a stop codon

Point Mutations

• Frameshift Mutations - DNA bases are inserted or deleted.

• “in/dels”

Point MutationsFrameshift Mutation:Extensive missense

The reading frame of the ribosome is altered so that all amino acidsdownstream from the in/del are altered

Point MutationsFrameshift Mutation:Immediate nonsense

The reading frame of the ribosome is altered so that a stop codon is introduced prematurely

Point Mutations

Frameshift Mutation:Limited Effect

The reading frame is restored when “in/del's” occur in multiples of three.

Sickle Cell Anemia

Mutations cause variation.Mutations are the ultimate source of variation in living systems.

Mutations and FitnessMutations only generate variation. Fitness is determined by the requirements of the environment.

Ex. Sickle cell Heterozygote Advantage.

Blame it on DNA