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

When are mutations inherited? Mutations will only be passed on to offspring if they occur in the gamete (sex cells) Results in genetic disorders

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 Types 1. GENE MUTATIONS— 2. CHROMOSOMAL 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 ATE CAT FAT RAT 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 ATE CAT FAT RAT TEF TET ATA ATC HER AT X

FRAMESHIFT MUTATION— INSERTION THE ATE CAT FAT RAT TAT TCA FLA 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

F E D A B C A C DELETION F E D

2. CHROMOSOMAL MUTATIONS b. DUPLICATION Opposite of deletion A segment of the chromosome is repeated

A B F E D A B C B F E D C DUPLICATION

2. CHROMOSOMAL MUTATIONS c. INVERSION Direction of genes is reversed within chromosome (part is upside-down)

F E D A B C A E D INVERSION C B F

2. CHROMOSOMAL MUTATIONS d. TRANSLOCATION When part of a chromosome breaks off and relocates to another part (non-homologous)

F E D A B C L K J G H I F E D A B C L K J G H I TRANSLOCATION

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