ChapterChapter

1212--44

DNADNA

MutationsMutations

What Are Mutations?What Are Mutations?

• Changes in the nucleotide sequence of DNA

• May occur in somatic cells (body cells) aren’t passed to offspring

• May occur in gametes (eggs & sperm) and can be passed to offspring

Mutations Helpful or Harmful?

• Mutations happen regularly• Almost all mutations are neutral (no effect)• Some can be harmful • Some can even be helpful!• Many mutations are repaired by enzymes

Mutations Helpful or Harmful?

• Chemicals & UV radiation cause mutations

• Some types of skin cancers and leukemia result from somaticmutations (harmful).

• Some mutations cause genetic variation which may improve an organism’s survival (beneficial)

Types of Mutations

1. Gene mutations- affects 1

gene only

2. Chromosomal mutations-affects parts of or whole chromosomes (many genes)

Gene Mutations

• Change in the nucleotide sequence of a gene

• May only involve a change in onenucleotide

• May be due to copying errors, chemicals, viruses, etc.

Types of GENE mutations

• Point mutation (3 types) a simple change at ONE point on DNA.

– Substitution

– Insertion

– Deletion

Examples of Gene Point Mutations

– Point Mutations-

1. Substitution (changes only 1 codon – this may or may not change the protein)

DNA=AGA���� mRNA=_____ codes for the amino acid (aa) ________

EX. Substitute the 3rd base with “C” So DNA =_____ and mRNA ���� ________ (aa=________)

Now Substitute the 1st base with a “C”, So DNA=_____

And mRNA ���� GCU (aa=________)

Serine

Serine

Alanine

ucu

UCG

AGC

CGA

2. Insertion Addition of one extra nitrogen base in the mRNA strand

- DNA = CTG AAG TCT TAG CTG

– mRNA= GAC UUC AGA AUC GAC

What are the AA’s

___________ ___________ ___________

____________ _____________

(insert a “T” after 5th base in DNA)

– How did it change mRNA?

– ______ ______ ______ ______ ______ _____

New AA’S ________ ___________ __________ __________ _________

GAC UUA CAG AAU CGA C

Aspartic acid Phenylalanine Arginine

Isoleucine Aspartic acid

Asparticacid leucine Glutamine

Asparagine Arginine

3. Deletion elimination of a nitrogen base on the mRNA strand

-DNA = TGC GGC ATG ACT

– mRNA= ACG CCG UAC UGA

What are the AA’s ________ _________ __________ __________

(Delete the 2nd base in DNA)

– How did it change mRNA? – ______ ______ ______ ______

New AA’S ________ ___________ __________

AGC CGU ACU GA

Threonine Proline Tyrosine Stop

Serine Arginine Threonine

–Frameshift- causes a shift in all codons after the point mutation.

• Which of the three point mutations could cause a frameshift?

–_________________

–_________________

INSERTION

DELETION

Point Mutation• Substitution in a sentence:– The fat cat ate the wee rat

substitute the “e” in ate to “t”

– The fat cat att the wee rat

– Doesn’t seem to change it much, but…

• Sickle Cell disease and Tay Sachsdisorder are both the result of one nucleotide base substitution.

Frameshift Point Mutation

• Insertion in a sentence:

– The fat cat ate the wee rat.

• (insert “a” before the “t” in cat):– The fat caa tat eth ewe era t

– This causes a ___________from the point of insertion.

frameshift

Amino Acid Sequence Changed

How would this change

Amino acid sequence?

Gene Mutation Animation

Click Here for Nova- ‘One Wrong Letter’

Chromosome Mutations

• May Involve:– Changing the structure of a

chromosome

– The loss or gain of part of a chromosome

Chromosome Mutations

–Deletion

–Inversion

–Translocation

–Nondisjunction

–Duplication

Deletion

• Due to breakage

• A piece of a chromosome is lost

Inversion

• Chromosome segment breaks off

• Segment flips around backwards

• Segment reattaches

Duplication

• Occurs when a gene sequence is repeated

Translocation

• Involves two chromosomes that aren’t homologous (pair of chromosomes that code for the same traits)

• Part of one chromosome is transferred to another chromosome

Translocation

Nondisjunction

•Failure of chromosomes to separate during meiosis

• Causes gamete to have too many or too few chromosomes

Chromosome Mutation Animation