Transcript Ch 12-4 - Latona

Ch 12-4
Genetic
Mutations
What is a Mutation?
• Changes in the genetic code of DNA
Original DNA: ATAGGCCTAGCAGTCG
Mutated DNA: ATAGGGCTAGCAGTCG
OR
Mutated DNA: ATAGGCCTAGCAAGTCG
OR
Mutated DNA: ATAGGCCTAGAGTCG
Mutations can occur in two different
types of cells:
• Somatic (body) cells
– Ex. Skin, heart, liver, lung, blood, muscle
• Gamete (sex/reproductive) cells
– Ex. Sperm, Egg
Mutations in somatic cells
• Usually result in killing that body cell only.
• Usually do not affect the individual.
– Exception: If the mutation occurs in the DNA
that controls the cell cycle (division), it can
result in cancer.
• Can NOT be passed on to the next
generation
Mutations in Gamete(sex) cells
• Means that every cell of the developing
fetus/baby will have that mutation.
• Usually do not affect the individual with
individual with the genetic disorder.
• Can be passed on to the next generation
There are two types of mutations
that can occur.
• Gene mutations
– Mutations that produce changes in a single
gene
• Chromosomal mutations
– Mutations that produce changes in parts of or
whole chromosomes.
Type of Single Gene Mutations POINT
Two Types of Single Gene
Mutations
• Point
• Frameshift
1. Point Mutation-a single point in
the DNA sequence is affected.
• Can be a substitution in which one base is
changed into another.
1. Point Mutation-a single point in
the DNA sequence is affected.
• Can be a substitution in which one base is
changed into another base during
replication.
• Example:
• Original Sequence
DNA:
TAC GCA TGG AAT
mRNA:
AUG CGU ACC UUA
Amino Acid: Met - Arg - Thr - Leu
(In this DNA sequence notice the 5th base in
the DNA sequence has been changed)
Mutated Sequence
DNA:
TAC GTA TGG AAT
mRNA:
AUG CAU ACC UUA
Amino Acid: Met - His - Thr - Leu
Point mutations usually affect no
more than a single amino acid.
• The protein may be slightly affected or not
affected at all.
• Ex using a sentence.
– THE FAT CAT ATE THE RAT
– THE FAT CAT ATE THE HAT
Types of Gene Mutations –
Frame Shift
2. Frame Shift Mutation
• A single gene or nitrogen base is deleted
or inserted from the mRNA sequence
causing a shift in the “reading frame” of
the genetic code.
• If a nucleotide is inserted or deleted, the
bases are still read in groups of three, so
every codon after is changed.
• Example:
• DNA:
TAC GCA TGG AAT
mRNA:
AUG CGU ACC UUA
Amino Acid: Met - Arg - Thr - Leu
*(Notice in this DNA sequence a T has been
added to the sequence after the second
base)
DNA:
TAT CGC ATG GAA T
mRNA:
AUA GCG UAC CUU A
Amino Acid: Iso - Ala - Tyr - Leu
• The affect of frame shift mutations is
usually more dramatic than point
mutations.
• Frameshift mutations may change
every amino acid that follows the point
of the mutation.
• Frameshift mutations can alter a
protein so much that it is unable to
perform its normal functions.
Example using a sentence
• THE FAT CAT ATE THE RAT
TEF ATC ATA TET HER AT
Chromosomal Mutations:
• Involves changes in the number or
structure of chromosomes
• Can change the locations of genes on
chromosomes, and the number of
copies of some genes
Chromosomal Mutations
5 types of Chromosomal
Mutations:
1.Deletion-Loss of all or part of a chromosome.
2.Duplication- extra copies of parts of the
chromosome are made.
3.Inversion- reverses the directions of parts of
a chromosome.
4.Translocation- Part of a chromosome breaks
off and attaches to another chromosome.
5.Non-disjunction- when chromosomes fail to
separate during meiosis.
Non-disjunction
• Results in abnormal numbers of
chromosomes. Typically you have 2 of
each.
– Trisomy (3) means a person has an extra
copy of a chromosome.
– Monosomy (1) means a person is missing a
copy of a chromosome.
What causes mutations?
• Usually during DNA replication.
• Sometimes from Environmental Factors
– UV radiation
– Chemicals (lead, asbestos)
– Pollution
– Tobacco smoke
– Viruses