All living organisms are made up of cells and each of our cells contains the same DNA (deoxyribonucleic acid) complement within their nucleus (genome).

DNA is a complex molecule that contains the information required for the development and maintenance of living organisms and is also responsible for hereditary transmission.

DNA is made up of four chemical units, called “nucleotides”, that are linked end to end to form a long chain.

These four nucleotides are symbolized as A, G, C, T, which stand for the four bases —adenine, guanine, cytosine, and thymine—that are parts of the nucleotides. The DNA molecule consists of two chains of nucleotides coiled around one another to form a double helix. The bases of one chain are linked to those of the other by hydrogen bonds and always pair in the same way. So, the adenine always links with thymine, and guanine always links with cytosine. This is referred to as complementary base pairing.

The genome size of an organism is considered as the number of total nucleotides in a “representative copy” of its nuclear DNA. The size of a “representative copy” of human genome is ~3 billion bases, while the size of the actual genome of an individual is ~6 billion bases.

The order of these bases in the DNA molecule is the so-called DNA sequence and it sets forth the genetic instructions necessary to develop and direct the activities of each organism.

The DNA segments that carry the information needed for protein synthesis are called genes.

DNA is arranged into structures known as chromosomes. Humans have 46 chromosomes in almost all their cells (somatic cells) arranged in 23 pairs, with one member of each pair inherited from each parent. Unlike the body's other cells, sex cells—egg and sperm —have only one set of chromosomes (23 chromosomes) and when they unite during fertilization, the double set number is restored (46 chromosomes).

What is DNA sequencing?
DNA sequencing is the process of determining the order of the four nucleotides (A, G, C and T) in the DNA molecule.

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