CHAPTER 14 SECTION 1Mutations

Are mutations good or bad?

Some mutations lead to genetic disorders

Some mutations may cause a beneficial trait

Some mutations are silent no effect good or bad.

Both!!

What is a Mutation? Mutation – a change

in the structure or amount of the genetic material in an organism A change in the DNA

A mutant is an individual whose DNA or chromosomes are different.

What causes mutations? When DNA replicates, mutations occur

accidently. DNA polymerase and other enzymes catch some

mistakes, but not all Very rare

Mutagens – substances that cause DNA to mutate Examples: radiation, UV light, chemical toxins

What are the effects of mutations?

Mutations may help, harm, or have no effect.

Depends on where the mutation occurs.

Depends on how much DNA is affected

Types of MutationsGene Mutations

Affect one geneChromosome mutations

Affect many genes

Point Mutations

Point Mutation – a change of a single nucleotide

Original MutatedDNA CTT CATRNA GAA GUAAmino acid

Glu Val

Silent Mutation Silent Mutation –

a mutation that has no effect on a gene’s function Why is this

possible?Because the

genetic code is so repetitive

Silent Mutation

DNA ATG CCT TCG A

RNA UAC GGA AGC U

Amino acid

Met Pro Ser Same AA sequence

Missense Mutation Missense Mutation –

a mutation that causes the codon to code for a different amino acid AKA – replacement

mutationMissense Mutation

DNA ATG CCT TCG CAT

RNA UAC GGA AGC GUA

Amino acid

Met Pro Ser Gln

Nonsense Mutation Nonsense mutation – a mutation that causes

a codon to change to a STOP codon Causes protein synthesis to stop early. Protein may not function

Nonsense Mutation

DNA ACG

RNA UGCUGA

Amino acid

Stop

Frameshift Mutation Frameshift Mutation – a mutation that causes

a shift in the reading frame. Reading frame – the sequence of codons from

start to finishFrameshift Mutation

DNA ATG CCA TCG

ATG GCC ATC G

RNA UAC GGA AGC

UAC CGG UAG C

Amino acid

Met Pro Ser

Met Ala Ile

Frameshift Mutation Insertion – adding

one or more nucleotides

Deletion – removing one or more nucleotides

What happens to the reading frame if 3 nucleotides are inserted or deleted?

Chromosomal Mutations Can occur during meiosis (crossing over)

Usually the homologous chromosomes exchange equally

Sometimes…they do not

Chromosomal Mutations Deletion – a piece of the chromosome is

lost Usually harmful

X-rays

Chromosomal Mutations Duplication – both pieces remain attached

to the same homologous chromosome

X-rays

Chromosomal Mutations Inversion – a piece attaches in the

opposite direction

ABCDEFGHIJKLMNOPABCDEFGHIJKLMNOP

ABCDEFGHIJKLMNOP

X-rays

Chromosomal Mutations Translocation – a piece ends up on a

completely different chromosome

X-rays

Chromosomal Mutations Gene Rearrangement – an entire gene is

moved to another location

X-rays

Nondisjunction Nondisjunction – occurs

when homologous chromosomes fail to separate One cell ends up with

extra chromosomes Down syndrome – extra

21 chromosome Aka – trisomy 21

Are mutations heritable? Mutations are only

inherited if the mutation occurs in the gamete (sperm and egg).

If a mutation occurs in one of your skin cell, it can affect you, but not your children.