What Is DNA?
DNA (deoxyribonucleic acid) is the genetic material of most living organisms and plays a central role in determining hereditary characteristics. DNA is a major component of the chromosomes found in the nucleus of each cell in the body and is also found in cell organelles called mitochondria (mitochondrial DNA). DNA consists of two complementary chains of molecules wound around each other in the form of a double helix. Each chain consists of molecules of the sugar deoxyribose linked by phosphate molecules. Attached to each sugar is one of four nucleotides or bases: adenine (A), thymine (T), guanine (G), and cytosine (C). The relationship between pairs of these nucleotides forms the basis for the complementary chain, in that adenine only pairs with thymine and guanine only with cytosine. This means that when the chains separate for replication each can form a complementary version of the other, resulting in two identical molecules.
What Is Human Genome?
Human cells have 22 pairs of matched (or homologous) chromosomes and a pair of sex chromosomes (XX, female or XY, male) that make up the genome, the entire complement of genetic material. Each chromosome consists of a single continuous strand of DNA, together with proteins known as histones that support the organization and packaging of the DNA. Genes, the units of heredity, consist of two components (or alleles), one of which is inherited from each parent. Around 25% of nuclear DNA is involved in the expression and regulation of genes. The remainder of the genome does not appear to play a role in gene expression and contains what is referred to as non-coding DNA. Amongst other things, the non-coding parts of the genome contain large amounts of DNA that consist of repetitive sequences. This includes tandem repeat DNA, of which short tandem repeats (STRs).