Page 9 - CB1.3 Genetic Varation sciPAD

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CB 1.3 GENETIC VARATION
PRINCIPLES OF GENETIC VARIATION
The Genetic Code
Each species has its own unique set of genes that make that particular species function in its own
unique way. The information stored in genes is written in a code, using a language that is the same
for all living things. DNA uses only four chemicals (called ‘bases’) that act as the code letters.
Cells are able to follow a gene’s instructions by reading this four-letter code. The four different
bases found in all DNA molecules are adenine (A), thymine (T), cytosine (C) and guanine (G). The
different chemical make-up of these bases means that adenine always bonds with thymine, and
cytosine always bonds with guanine. This specific pairing of bases is called the ‘complementary
base-pairing rule’. The difference between one gene and another is the order of these bases.
1. Describe the ‘complementary base-pairing rule’. 


2. Use the complementary base-pairing rule to complete the section of DNA below:
Making a DNA Molecule
1. Cut out the pieces of the DNA molecule below.
2. Read and complete the following page on ‘Nucleotides’.
3. Assemble the model on the previous page by gluing the bases next to a sugar (S) and
linking the phosphates (P).
4. Construct a key to identify the different parts of the molecule represented by the letters.
G T
C
P
S
P
S
P
S
P
S
P
S
P
S
P
S
P
S
A G C
T
A
T A C A
C T G A
G A T T C
C G C A G
C C G T G
A Apples in the T Tree
C Cars in the G Garage
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