Genetic Mutations

Mutation:An unpredictable change in the genetic

material of an organism

Gene Mutation:A change in the structure of a DNA molecule,

producing a different allele of a gene (allele = version of a gene; ex: brown hair,

black hair)

Chromosome Mutation: A change in the entire structure or number of

whole chromosomes

Causes of Mutations

Mutations occur randomly with no obvious cause.

Mutagens: Substances that increase the chances

of mutation occurring

Types of Mutations

• Base Substitution – One nucleotide base takes the place of another

• One amino acid is changed in the sequence

Base Substitutions

• Missense = if substitution changes amino acid

• Nonsence = if substitution changes amino acid into a “stop” codon

Types of Mutations

• Base Addition – (aka Insertions) One or more extra nucleotide bases added to a sequence

• Base Deletion – One or more nucleotide bases are lost from the sequence

**Both additions and deletions cause

Frame Shift Mutations

• Incorrect sequence of amino acids

• Incorrect sequence of amino acids• Frame Shift Mutations

Silent mutations – Mutation that has no apparent effect on an organism OR does not change the amino acid

Which types of mutations have the greatest impacts?

Sickle Cell Anemia

Sickle Cell Anemia• Base substitution with a significant side effect on

phenotype

• The affected gene codes for the oxygen carrying pigment HAEMOGLOBIN.

Normal Amino Acid Sequence:Val-His-Leu-Thr-Pro-Glu-Glu-Lys-

Sickle Cell Anemia Sequence:Val-His-Leu-Thr-Pro-ValVal-Glu-Lys-

• When haemoglobin is not combined with oxygen, the β chains are less soluble causing them to stick to each other.

• This pulls RBC’s out of shape into a sickle shape.

Phenylketonuria (PKU)

• Base substitution

• The affected gene codes for an enzyme (phenylalanine hydroxylase), which is not present in people with the mutation

• This enzyme helps catalyse the conversion of phenylalanine to triosine, which is then converted to melanine

Effects of PKU

• Lighter skin colour

• Accumulation of phenylalanine in blood and tissue fluid, causing severe brain damage

• Babies are tested for PKU at birth for prevention

Environmental Impacts on Phenotype

• Some alleles code for traits that are highly impacted by environmental factors, such as height.

• Diet

• Temperatures