Genetic Mutations

Standards:

• CLE 3210.4.6 Describe the connection between mutations and human genetic disorders.

Objectives:• Investigate the affect of mutations on protein

production• Differentiate between point mutations and

chromosomal mutations.

What is a gene mutation?

• Mutations are changes in genetic material – changes in DNA code – which means changes in a gene(s)

• In gene mutations, the DNA code will have one or more bases missing, added, or exchanged in a codon.

How common are mutations?

• Mutations occurs at a frequency of about 1 in every 1 billion base pairs

• Everybody has about 6 mutations in each cell in their body!

Does that mean I have a chance to become a super hero/villian?

If I have that many mutations, why don’t I look weird?

• Mutations are not always seen. The affected gene may still function.

• Mutations may be harmful.

• Mutations may be beneficial.

• Mutations may have no effect on the organism.

How do mutationsaffect a population?

• Mutations are a major source of genetic variation in a population increasing biodiversity.

• Some variations may help them to survive better.

Beneficial or Harmful?

How are mutations inherited?

Only mutations that occur in gametes are passed onto offspring.

Mutations in body cells (somatic cells) only affect the organism in which they occur and are not passed on.

Types of Gene Mutations

• Point mutation occurs when the base sequence of a codon is changed. (ex. GCA is changed to GAA)

• Chromosome mutations - Changes in the number or structure of chromosomes

Types of Point Mutations• Point mutation occurs when the base

sequence of a codon is changed. (ex. GCA is changed to GAA)

• There are 3 types:

Also called frameshift mutations

•Substitution

•Deletion

•Insertion

What will happen to the amino acids?

Substitution Mutations

Normal DNA: CGA – TGC – ATC

Mutated DNA: CGA – TGC – TTC

Alanine – Threonine - stop

Alanine – Threonine - Lysine

This is a substitution mutation

The adenine was replaced with thymineWhat has happened to

the DNA?

Substitution Mutations• This is a substitution mutation.

• A single nitrogen base is substituted for another in a codon.

• It may or may not affect the amino acid or protein.

Mutated DNA: CGA – TGC – TTC

Alanine – Threonine - Lysine

Normal DNA: CGA – TGC – ATC

Alanine – Threonine - stop

TRY THIS!

• On your note paper write:The cat ate the rat

• Change one letter in the sentence to represent a substitution mutation.

Think – Pair - Share• Why are we using 3 letter words?

• Share with your partner the substitution change that you made

• Can you still “read” your sentence fairly easily?

• How damaging is a substitution mutation?

Analogy

The cat ate the rat.

SUBSTITUTION #1

Thc cat ate the rat.

May have little effect. You can still get the overall idea. Like a typo on a test.

SUBSTITUTION #2

The hat ate the rat.

Changes the thought of the sentence.

The effect of the mutation depends on where the substitution happens

This is an insertion mutation, also a type of

frameshift mutation.

Insertion Mutations

Normal DNA: CGA – TGC – ATC

Mutated DNA: CGA – TAG – CAT – C

Alanine – Threonine – stop

Alanine – Isoleucine – Valine

What will happen to the amino acids?

An adenine was inserted thereby pushing all the

other bases over a frame.

What has happenedto the DNA?

Insertion Mutations• This is an insertion mutation.

• A nitrogen base is inserted/added to the sequence.

• It causes the triplet “frames” to shift.

• It always affects the amino acids and, consequently, the protein.

Mutated DNA: CGA – TAG – CAT – CAlanine – Leucine - Valine

Normal DNA: CGA – TGC – ATC Alanine – Threonine - stop

Think – pair - share

• Predict the effect an insertion mutation cause to our sentence:

THE CAT ATE THE RAT

TRY THIS!

• On your notebook paper write:The cat ate the rat.

• Insert a letter into any word above.• Rewrite the sentence . Each word must

have only 3 letters to represent the codon. • What were the effects of the insertion?

AnalogyThe cat ate the rat.

Insertion

The cca tat eth era t.

Inserting the c causes a

FRAMESHIFT

THE SENTENCE NO LONGER MAKES SENSE!!

Think – pair - share• Where in the gene sequence would an

insertion mutation cause the most damage to the DNA code?

At the beginning of the gene sequence

Let’s examine the effect of locationTHE CAT ATE THE RAT

INSERTION #1– THE CAT ATE THA ERA T

– Would any of the codons code correctly?

INSERTION #2– TAH ECA TAT ETH ERA T

– Would any of these codons code correctly?

What will happen to the amino acids?

Mutated DNA: CGA – TCA- TC

A guanine was deleted, thereby pushing all the bases down a frame.

Alanine – Threonine – stop

Alanine – Serine

Deletion Mutations

Normal DNA: CGA – TGC – ATC

This is called a deletion mutation, also a type of

frameshift mutation.

What has happenedto the DNA?

Deletion Mutations• This is a deletion mutation.

• A nitrogen base is deleted/removed from the sequence.

• It causes the triplet “frames” to shift.

• It always affects the amino acids and, consequently, the protein.

Mutated DNA: CGA – TCA- TCAlanine – Threonine – stop

Alanine – Serine

Normal DNA: CGA – TGC – ATC

TRY THIS!

• Write the sentence on your paper:

The cat ate the rat.

• Delete one letter from any word.

• Rewrite the sentence. Remember: each word can only have 3 letters.

AnalogyDELETION

The cat ate the rat.

Thc ata tet her at

FRAMESHIFT

The sentence no longer makes sense!! Deletions can have huge

effects.

Standards:

• CLE 3210.4.6 Describe the connection between mutations and human genetic disorders.

Objectives:• Investigate the affect of mutations on protein

production• Differentiate between point mutations and

chromosomal mutations.

Think – pair - share

• Which type of mutation would have the least damaging affect on an organism?

• Substitution has the least affect because it changes only one amino acid or it may change no amino acid.

Mutated DNA: CGA – TGC – ATTAlanine – Threonine - stop

Normal DNA: CGA – TGC – ATC Alanine – Threonine - stop

Mutated DNA: CGA – TGC – ATGAlanine – Threonine - Tyrosine

An example of a substitution mutation is sickle cell anemia

• Only one amino acid changes in the hemoglobin.

• The hemoglobin still functions but it folds differently changing the shape of the rbc.

Think – pair - share• Which type(s) of mutation would have the most

affect on an organism?

• Insertion and deletion mutations have the most effect on an organism because they affect many amino acids and consequently the whole protein.

Mutated DNA: CGA – TCA- TCAlanine – Threonine – stop

Alanine – Serine

Normal DNA: CGA – TGC – ATC

Mutated DNA: CGA – TAG – CAT – CAlanine – Leucine - Valine

An example of a frameshift mutation disorder is Tay Sachs disease.

• Children born with this disorder cannot make an enzyme that is critical in breaking down fat and toxic substances in the brain.

• The disease is terminal. Most will die before age 4.

Think – pair - share

• In which cells would a gene mutation have the greatest affect on an organism?

• When it is inherited from the gametes or develops early in embryonic development (in stem cells or first few days). Four cell Zygote

Embryo

Egg being fertilized

Mutagens

• What causes mutations?– natural errors during replication– an environmental mutagen/carcinogen

• What is a mutagen (carcinogen)? something that causes the DNA code to

change (mutate) – x-ray, chemicals, UV light, radiation, etc

• What happens to a person who has a mutation?

Gene Mutations Activity

• Complete the worksheet

Chromosomal Mutationsthink – pair - share

• How do you think we could mutate a chromosome?

• List at least 3 ways

Chromosomal Mutations• Changes in the

number or structure of chromosomes

• Deletions

• Duplication

• Inversion

• Translocation

• Nondisjunction

Deletions• removal of a gene and/or entire chromosome

Duplication

• repeat of a gene or chromosome

Inversion

• gene sequences are switched on the chromosome

Translocation• part of one chromosome breaks off and

reattaches to a non-homologous chromosome

Think - pair - share

• Compare and contrast translocation with crossing – over–How are they similar?–How are they different?

Non-disjunction• A chromosome fails to separate from its

homologue during meiosis

Down’s Syndrome• Result of nondisjunction of the chromosomes

at pair #21

Homework

• Chromosome Mutation activity

Standards:• CLE 3210.4.6 Describe the connection

between mutations and human genetic disorders.

Objectives: (DID WE…)• Investigate the affect of mutations on protein

production• Differentiate between point mutations and

chromosomal mutations.

Exit Ticket

• How do mutations affect the production of a protein?