Section 12 – 4Mutations

Key Concept:Gene mutations result from changes in a single gene. Chromosomal mutations involve changes in whole chromosomes

Point Mutations Affect one nucleotide Occur at a single point

in the gene sequence Three Types:

1. Deletion2. Insertion3. Substitution

Frameshift MutationsResult From

Insertions & Deletions

A nucleotide is added, or subtracted from the nucleotide sequence. This shifts the Codon grouping and drastically alters the amino acid sequence in the protein.

SubstitutionA single nucleotide is changed in the

nucleotide sequence.This may result in a change to a single amino acid in the protein.

The change to a single amino acid may or may not alter the proteins function.

CodonCodon == Amino AcidAmino Acid

UGUUGU OriginalOriginal CysteineCysteine

UGUGCC No No ChangeChange CysteineCysteine

UUGGGG Single Single AAAA TryptophanTryptophan

UUGGAA BadBad STOPSTOP

Changes the number or structure of chromosomes

May change locations of genes on chromosome or the number of copies of some genes

4 Types

1. Deletion2. Duplication

3. Inversion4. Translocation

DeletionLoss of all or part of a

chromosome

X

DuplicationSegment of chromosome is

repeated

InversionInversionChromosome or part of a Chromosome or part of a

chromosome is oriented in the chromosome is oriented in the reverse directionreverse direction

TranslocationTranslocationPart of one chromosome breaks Part of one chromosome breaks

off and attaches to another, off and attaches to another, nonhomologousnonhomologous chromosome chromosome