MUTATIONS

MUTATIONS• The alteration of an organism’s

DNA• Wide range of mutations• Most mutations are

automatically repaired by the organism’s enzymes…

• …therefore they have no effect.

MUTATIONS• However…when the mutation

is NOT repaired…• The resulting altered

chromosome/gene structure is passed to ALL subsequent daughter cells of the mutant cell…

• Mutations can be good or bad.

When are mutations inherited?

• Mutations that occur in regular body cells (somatic cells) will affect all daughter cells, but will not be passed to offspring• Can contribute to aging

process• May lead to cancer…

When are mutations inherited?

For example:

• Mutation in lung cell will lead to cancer, but cancer isn’t passed on to offspring

• Mutations will only be passed on to offspring if they occur in the gamete (sex cells)

• Results in genetic disorders

When are mutations inherited?

When are mutations inherited?

• Lethal mutations result in the death of the organism• Often miscarriage

What causes mutations?

• Malfunction during the process of meiosis

• Exposure to a physical or chemical agent

• Called a mutagen

• Examples: x-rays, chemicals (asbestos, formaldahyde), UV rays,

Two Types1. GENE MUTATIONS—

• changes in a single gene (a segment of DNA)

2. CHROMOSOMAL MUTATIONS—• changes in whole chromosomes

(chromosome number or chromosome itself)

1. GENE MUTATIONS

a. POINT MUTATION (Substitution)

• Single nucleotide is substituted for the wrong one

• Ex: A-G instead of A-T

• This can lead to…

1. GENE MUTATIONS

1) Silent mutation: has NO effect since some amino acids have multiple sequences

Ex: CUC codes for leucine

CUA also codes for leucine

1. GENE MUTATIONS

2) Missense mutation: causes the wrong amino acid to be in sequence

Ex: CUU codes for leucine

CCU codes for proline

1. GENE MUTATIONS

3) Nonsense mutation: causes an early STOP codon

Ex: UCA codes for serine

UGA codes for STOP

POINT MUTATION—SUBSTITUTION

THE ATECATFAT THE RAT

THE ATECATFAT THE HAT

1. GENE MUTATIONS

b. FRAMESHIFT MUTATION

• insertion or deletion of one or more nucleotides

• All codons are shifted

• May cause serious effects

• Such mutations can alter a protein so that it is unable to perform its normal functions.

FRAMESHIFT MUTATION— DELETION

THE ATECATFAT THE RAT

THE ATECATFAT THE RAT

TEF TETATAATC HER AT

X

FRAMESHIFT MUTATION— INSERTION

THE

THE ATECATFAT THE RAT

THE ATECATFAT THE RAT

TATTCAFLA ETH ERA T

Disorders caused by GENE MUTATIONS

• Sickle-cell disease

• Tay-Sachs disease

• Huntington’s disease

• Cystic Fibrosis

• Albinism

2. CHROMOSOMAL MUTATIONS

a. DELETION

• Involves loss of a part or whole chromosome

DELETION

FED

ABC

FED

AC

2. CHROMOSOMAL MUTATIONS

b. DUPLICATION

• Opposite of deletion

• A segment of the chromosome is repeated

DUPLICATION

FED

ABC

AB

FED

CB

2. CHROMOSOMAL MUTATIONS

c. INVERSION

• Direction of genes is reversed within chromosome (part is upside-down)

INVERSION

FED

ABC

F

ED

A

BC

2. CHROMOSOMAL MUTATIONS

d. TRANSLOCATION

• When part of a chromosome breaks off and relocates to another part (non-homologous)

TRANSLOCATION

FED

ABC

LKJ

GH

I

FED

ABC

LKJ

GH

I

2. CHROMOSOMAL MUTATIONS

e. NONDISJUNCTION

• Results in too few or too many chromosomes in a cell…

NONDISJUNCTION

• MONOSOMY•Having only ONE copy of a chromosome instead of TWO

•EX: Turner’s syndrome (has only one X chromosome)

NONDISJUNCTION

• TRISOMY•Having THREE copies of a chromosome instead of TWO

•EX: Down Syndrome (3 copies of chromosome #21, trisomy 21)

NONDISJUNCTION

Disorders caused by CHROMOSOMAL MUTATIONS

• NONDISJUNCTION of Sex Chromosomes:

• Klinefelter’s syndrome (male)

• Turner’s syndrome (female)

• NONDISJUNCTION of Autosomal Chromosomes:

• Down Syndrome (Trisomy 21)

Where can mutations occur?

Somatic Cells (Body Cells)

Germ Cells (Sex Cells)

Somatic Cells (Body Cells)

• During or before mitosis

• All new cells will also be altered

• The change is permanent

• Only effects organism, not offspring

Germ Cells (Sex Cells)

• Changes can occur in egg/sperm before, during or after meiosis

• Altered egg/sperm may be fertilized—passing change to offspring

• Changes may or may not be harmful

• Harmful changes cause birth defects