Genes as Sections of DNA Molecules

Genes are the building blocks of inheritance and are located on chromosomes. They determine the characteristics of an organism.
Each gene is a specific segment of a DNA molecule and contains an individual set of instructions for the production of a particular protein within a cell.
DNA is a molecule made up of two strands coiled together in a double helix structure. Each strand is made up of a sequence of molecules called nucleotides.
A nucleotide is composed of a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base, which could be adenine (A), guanine (G), cytosine (C), or thymine (T).
The double helix structure of the DNA molecule is formed through hydrogen bonds that link the nucleotides of one strand to those of the other strand in a specific way - adenine (A) forming bonds with thymine (T), and guanine (G) forming bonds with cytosine (C). This is known as complementary base pairing.
The sequence of bases A, T, C, and G in a DNA molecule determines the genetic information it carries. This is similar to how letters of the alphabet can be lined up in a particular order to form words with different meanings.
A sequence of three bases in a DNA molecule, called a triplet, codes for a specific amino acid. Each triplet is a unit of genetic code. The order of these triplets determines the order of amino acids in the protein being synthesised.
The proteins formed carry out a wide variety of functions in the body. For example, enzymes are proteins that speed up biological reactions, and some proteins provide structural support for cells.
Genes and the variation in their base sequences provide the basis for genetic diversity in life on Earth. Genetic variation arises from mutations, which are changes in the base sequence of the DNA molecule. Some of these changes can be beneficial, opening up new opportunities for evolution.