GEN

ETIC MU

TATION

S

Sexual Reproduction

• Results in variations • Variations help

organisms adapt – Allow breeders to

develop new strains of plants/animals

• Most variations come from segregation and crossing over in meiosis

Source of Variations• Most variations come from:– Segregation– Crossing over

Mutations

• Mutations are sudden changes in the structure or amount of genetic material

• Most mutations are harmful; some are beneficial (i.e. ones that allow species to meet needs of environment)

Types of Mutations

• 2 Main Types:– Chromosome Mutation = changes

structure of all/part of chromosome– Gene Mutation = affects a gene on

a chromosome• Mutation must be in DNA of sex

cells in order for it to be passed on.

• Mutations in body cells can’t be passed on.

What Causes Mutations

• Random error in DNA replication

• Environmental Factors (called mutagens)– Radiation (X-rays)– UV light– Chemicals (chloroform

and mustard gas)

Chromosome Mutations

1) Translocation• One part of a chromosome is transferred to a

non-homologous chromosome

Chromosome Mutations

2) Inversion• One part of a chromosome is rotated (reverses

order of genes)

Chromosome Mutations

3) Addition• One part of a

chromosome breaks off and attaches to a homologous chromosome

Chromosome Mutations

4) Deletion• One part of a chromosome breaks off. This

results in a loss of some genes• E.g. Angleman’s Syndrome (Chromsome #15)

Chromosome Mutations5) Non-disjunction• Addition or loss of a whole chromosome (ones

that usually separate during meiosis remain together)

Chromosome Mutations

6) Polyploidy• More than normal copy of chromosomes

Gene Mutations

• Genes tell the cell what order to arrange amino acids (to form proteins)

• Changes in the DNA sequence will change the message transcribed into mRNA & likely change the protein

• Types of Mutations:– Point Mutation– Base Substitution

Point Mutation

• Single nucleotide in a gene is changed• This is drastic as all triple codons beyond are

changed• This makes the gene useless and the organism

will lack the protein normally made by the gene

Base Substitution

• One base in a nucleotide is substituted for another.

• This changes 1 codon and one amino acid• Results in a protein that doesn’t function

normally• E.g. PKU– Substitution of GT to AT