Mutations
- Mutations are permanent changes to one or
more nucleotides in the DNA sequence.
- A beneficial
mutation gives the organism a selective advantage and can lead to new
evolutionary changes of a particular genotype.
- A harmful
mutation will reduce the individual’s fitness and tends to be selected against.
These mutations cause disease,
developmental delays, structural
abnormalities etc…
- Can
occur in somatic cells (not passed to
offspring) or in gametes (egg and sperm)
and are passed to offspring.
Potential causes of mutations
Mutagens are physical or chemical agents that cause mutations in DNA
2 types of factors that cause mutations:
External- 1. environmental factors- sunlight, UVB radiation, nuclear radiation, x-rays and smoking
2. Chemicals- formalin and benzene
Internal- errors in DNA replication (i). Chromosomal abnormalities during construction
(ii) Genetic changes brought about by errors in DNA replication
2 types of factors that cause mutations:
External- 1. environmental factors- sunlight, UVB radiation, nuclear radiation, x-rays and smoking
2. Chemicals- formalin and benzene
Internal- errors in DNA replication (i). Chromosomal abnormalities during construction
(ii) Genetic changes brought about by errors in DNA replication
Types of mutations
Types of Mutations:
KEY TO TABLE:
The original sequence is shown on the top
the mutated sequence shown below it.
The genetic sequence is shown in black while the protein sequence is in blue.
Changes in sequence are highlighted by yellow.
KEY TO TABLE:
The original sequence is shown on the top
the mutated sequence shown below it.
The genetic sequence is shown in black while the protein sequence is in blue.
Changes in sequence are highlighted by yellow.
Outline of different types of mutations
There are two types of mutations
that can occur in gamete cells:
1. Gene Mutations
2. Chromosomal Mutations
1. GENE MUTATIONS
DNA replication is protected by base pairing BUT ERRORS can still occur WHILE THE DNA IS BEING COPIED, especially if someone is exposed to mutagens such as radiation and some chemicals.
The result may be that a gene is wrongly expressed and the particular protein is either not made or a faulty one is produced.
a gene mutation alters a single gene or larger segment of DNA on a chromosome.
1. Gene Mutations
2. Chromosomal Mutations
1. GENE MUTATIONS
DNA replication is protected by base pairing BUT ERRORS can still occur WHILE THE DNA IS BEING COPIED, especially if someone is exposed to mutagens such as radiation and some chemicals.
The result may be that a gene is wrongly expressed and the particular protein is either not made or a faulty one is produced.
a gene mutation alters a single gene or larger segment of DNA on a chromosome.
The
instructions for a particular code are not followed as they should be. This
leads to incorrect base pairing.
- Substitution of a different nucleotide
- Deletion or insertion of a nucleotide
- THESE ARE CALLED POINT MUTATIONS and
they change the genetic message because they will code for different amino
acids. Different or non functional protein is the result. THIS AFFECTS THE
PHENOTYPE OF THE ORGANISM.
Eg…. Sickle cell anaemia disease is a gene mutation with altered polypeptide chains caused by amino acid substitutions.. Adenine base is substituted by a thymine base. The phenotype of the normal red blood cell changes in shape.
2 types of single gene mutation
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.
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.
THE FAT CAT ATE THE RAT
THE FAT CAT ATE THE HAT
2. Frame shift Mutation: a single gene or nitrogen base is deleted or added from the mRNA sequence causing a shift in the “reading frame” of the genetic message.
Can be an insertion in which one base is inserted in the DNA sequence.
Can be a deletion in which one base is deleted in the DNA sequence.
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 Effect of frameshift mutations is usually more dramatic. 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.
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Can be a substitution in which one base is changed into another base.
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.
THE FAT CAT ATE THE RAT
THE FAT CAT ATE THE HAT
2. Frame shift Mutation: a single gene or nitrogen base is deleted or added from the mRNA sequence causing a shift in the “reading frame” of the genetic message.
Can be an insertion in which one base is inserted in the DNA sequence.
Can be a deletion in which one base is deleted in the DNA sequence.
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 Effect of frameshift mutations is usually more dramatic. 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.
THE FAT CAT ATE THE RAT
THE FAT CAT ATE THE RAT
TEF ATC ATA TET HER AT
CHROMOSOMAL MUTATIONS
- unpredictable
changes that happen in a chromosome,
usually during meiosis. chromatids fail
to separate so are born with an extra
chromosome or part of a chromosome. (number
and structure of chromosomes are affected/changed).
- These
changes affect protein production by changing the genes on the chromosome
- Chromosomes
may be deleted, added or a mixing of genetic information from
segments of chromosomes can occur.
- The
breaking and duplication of chromosomes alters chromosome structure.
5 types of Chromosomal
Mutations:
1.Deletion: Involves the loss of all or part of a chromosome.
2.Duplication: Involves the production of extra copies of parts of the chromosome
3. Inversion: Reverses the direction of parts of a chromosome.
4. Translocation: When one part of a chromosome breaks off and attaches to another chromosome.
5. Non-disjunction: Means “not coming apart”. When homologous chromosomes fail to separate
1.Deletion: Involves the loss of all or part of a chromosome.
2.Duplication: Involves the production of extra copies of parts of the chromosome
3. Inversion: Reverses the direction of parts of a chromosome.
4. Translocation: When one part of a chromosome breaks off and attaches to another chromosome.
5. Non-disjunction: Means “not coming apart”. When homologous chromosomes fail to separate
RELATIONSHIP BETWEEN MUTATIONS AND GENETIC VARIATION
- Mutations cause variations that will help an individual
survive.
- New and different
types of alleles are created on a gene
which will change the DNA SEQUENCE and this will make every person unique, because
the genotype ranges are increased, and
this increases variation..
- Differences can be
seen in physical appearance, behaviour, height,
hair colour, skin colour etc….
- This genetic
variation can help a population survive and reproduce and these favourable
traits can be passed down to the next generation. Unfavourable variations get
removed from the population.
- This is natural
selection and can provide good changes like physical makeup of a person, and
behaviour to be passed down to future generations.
- New alleles will combine
during meiosis and sexual reproduction in new ways to increase genetic
variation.
Image :( Purna, A. 2011)