Page 65 - CB1.3 Genetic Varation sciPAD

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CB 1.3 GENETIC VARIATION
USING KNOWLEDGE OF GENETICS
DNA Sequencing
DNA sequencing refers to the process of identifying the exact order
of bases in a strand (or gene) of DNA.
One of the original DNA sequencing methods used for many years
was developed by Frederick Sanger in 1977, and was the DNA
sequencing method of choice until the mid 2000s.
Modern sequencing machines produce four colour
‘chromatograms’ - graphs of the DNA sequences where each
DNA base is represented as a peak of a different colour: adenine
(green), cytosine (blue), guanine (black), and thymine (red). A typical
chromatogram contains 1000 to 1200 bases.
DNA sequencing can be used for genetic screening. Genetic screening is the process of
sequencing a section of DNA to identify mutations in genes that can cause or increase the risk of
a disease such as cancer.
1. Describe in your own words what is meant by the sentence: “DNA sequencing refers to the
process of identifying the order of bases in a strand (or gene) of DNA”. 



2. The chromatogram below shows the base sequence of a gene. The gene contains a
mutation that increases the likelihood of developing skin cancer (melanoma). It was taken
from a woman who had developed, and been treated for melanoma.
A G G G G G G G G
G G
C C C C C C
C C C T T T
T
A A
Chromatograms for the same gene from her two children are shown below.
(a) Analyse the children’s chromatograms and state whether either of her children
carry the mutation. Justify your answer.



(b) Suggest how using DNA sequencing technology in this way could lead to better
health outcomes for her children. 



A G G G G G G G G
G G
C C C C C C
C C C T T T
T
A A
Child 1
A G G G G G G
G G
C C C C C C
C C C T T T
T
A A A A
Child 2
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