BIOLOGY DEPTH STUDY
INVESTIGATING MUTATIONS
~ZOYA ADNAN
PART A:
1) Define point/gene mutation
A point mutation is a change to the gene where the single base pair sequence of DNA is
altered. This can usually occur when mistakes happen during DNA replication or through
modifications occurring through exposure to radiation which induce point mutation.
2) Describe what happens during a base substitution.
During base substitution, one nucleotide is swapped with another during DNA replication,
and since only one nucleotide has been swapped, only one codon is affected. The change can
still have an effect on the production of the protein as the codon then codes for a different
amino acid. For example, a thymine nucleotide may be swapped with cytosine.
3) Distinguish between silent, missense and nonsense mutation. Describe the possible
effects of each on the phenotype.
Silent mutation: are the changes in the genetic code that do not have an effect on the amino
acids. Silent mutations still involve the swapping of nucleotide but the change does not affect
the protein as the codon still codes for the same amino acid. For example, GCC changes to
GCA which both code for the amino acid valine, and thus it does not affect the polypeptide
sequence of amino acid. Hence, there is no noticeable effect on the phenotype.
Missense mutation: unlike silent mutation, the change in nucleotide results in coding of a
different amino acid than the original. This results in the protein functionality being altered
and the original function is changed. Therefore, the phenotype of an organism is expressed as
highly heterogenous. The most common missense mutation is sickle-cell-amenia, which is a
blood disease.
Nonsense mutation: compared to silent and missense, nonsense mutation is a result in a
change in amino acid to code a stop codon which completely makes the protein non-
functional as the protein is cut short. This has a major effect on the phenotype. An example is
Duchenne muscular dystrophia which is a genetic disease.
, 4) What is meant by frameshift mutation? What are the 2 main causes?
A frameshift mutation is genetic mutation through a deletion or insertion in DNA sequence
which shifts the way its read. Codons are put in triplets as they are read in threes by mRNA.
When the codon is altered, the protein becomes non-functional.
5) Find out about the different type of chromosome rearrangements. What are the
effects? Find examples of each type in humans and give a brief description of the
disease/disorder that it causes.
Chromosomal mutations are where the chromosome structure changes or the overall number
of chromosomes in a cell is altered. There are four types of chromosomal rearrangements:
deletion, duplication (insertion), translocation and inversion.
Deletion: a chromosomal deletion occurs when a section of the DNA is removed and not
replaced back in. This causes a reduction in the number if genes in a chromosome. This can
cause effect on the organism, having severe anomalies and can cause intellectual and physical
disability. An example within humans is cri-du-chat syndrome, also known as 5p minus
syndrome which occurs when a piece of chromosome 5 is missing. This results in an infant
with a high-pitched cry that sounds like a cat.
Duplication: chromosomal insertion is when a portion of DNA is doubled or duplicated,
increasing the number of genes on a chromosome. The effects depend on the size, location
and number of repeats. The increased number of genes can lead to excess of proteins. An
example is Huntington’s disease which is a progressive brain disorder, which affects the
central area of the brain, effecting movement, thinking and mood.
INVESTIGATING MUTATIONS
~ZOYA ADNAN
PART A:
1) Define point/gene mutation
A point mutation is a change to the gene where the single base pair sequence of DNA is
altered. This can usually occur when mistakes happen during DNA replication or through
modifications occurring through exposure to radiation which induce point mutation.
2) Describe what happens during a base substitution.
During base substitution, one nucleotide is swapped with another during DNA replication,
and since only one nucleotide has been swapped, only one codon is affected. The change can
still have an effect on the production of the protein as the codon then codes for a different
amino acid. For example, a thymine nucleotide may be swapped with cytosine.
3) Distinguish between silent, missense and nonsense mutation. Describe the possible
effects of each on the phenotype.
Silent mutation: are the changes in the genetic code that do not have an effect on the amino
acids. Silent mutations still involve the swapping of nucleotide but the change does not affect
the protein as the codon still codes for the same amino acid. For example, GCC changes to
GCA which both code for the amino acid valine, and thus it does not affect the polypeptide
sequence of amino acid. Hence, there is no noticeable effect on the phenotype.
Missense mutation: unlike silent mutation, the change in nucleotide results in coding of a
different amino acid than the original. This results in the protein functionality being altered
and the original function is changed. Therefore, the phenotype of an organism is expressed as
highly heterogenous. The most common missense mutation is sickle-cell-amenia, which is a
blood disease.
Nonsense mutation: compared to silent and missense, nonsense mutation is a result in a
change in amino acid to code a stop codon which completely makes the protein non-
functional as the protein is cut short. This has a major effect on the phenotype. An example is
Duchenne muscular dystrophia which is a genetic disease.
, 4) What is meant by frameshift mutation? What are the 2 main causes?
A frameshift mutation is genetic mutation through a deletion or insertion in DNA sequence
which shifts the way its read. Codons are put in triplets as they are read in threes by mRNA.
When the codon is altered, the protein becomes non-functional.
5) Find out about the different type of chromosome rearrangements. What are the
effects? Find examples of each type in humans and give a brief description of the
disease/disorder that it causes.
Chromosomal mutations are where the chromosome structure changes or the overall number
of chromosomes in a cell is altered. There are four types of chromosomal rearrangements:
deletion, duplication (insertion), translocation and inversion.
Deletion: a chromosomal deletion occurs when a section of the DNA is removed and not
replaced back in. This causes a reduction in the number if genes in a chromosome. This can
cause effect on the organism, having severe anomalies and can cause intellectual and physical
disability. An example within humans is cri-du-chat syndrome, also known as 5p minus
syndrome which occurs when a piece of chromosome 5 is missing. This results in an infant
with a high-pitched cry that sounds like a cat.
Duplication: chromosomal insertion is when a portion of DNA is doubled or duplicated,
increasing the number of genes on a chromosome. The effects depend on the size, location
and number of repeats. The increased number of genes can lead to excess of proteins. An
example is Huntington’s disease which is a progressive brain disorder, which affects the
central area of the brain, effecting movement, thinking and mood.
