Chromosomes - DNA is contained in molecules known as chromosomes. Each individual has 46 total chromosomes or 23 pairs - one of each pair comes from each parent. 22 pairs of chromosomes contain what is called autosomal DNA and the 23rd pair contains DNA that determines the gender of the child. A male is XY and a female is XX. A routine parentage test examines non-coding regions of the autosomal DNA but also examines a section of the 23rd pair of chromosomes to determine if the tested individual is male or female. Our Y-STR test examines the DNA that is present on the Y-chromosome, which is present only in males.

Double Helix – On a more microscopic level, the chromosomes are actually made up of DNA that is present as a double-stranded molecule called a double helix.

Nucleotides - The DNA double helix is a long chain of molecules. Each molecule is formed from the nucleotides (bases) that are like letters of the alphabet. However while the English alphabet has 26 letters, the DNA alphabet has only four letters called nucleotides or bases:

• Adenine (A)
• Thymine (T)
• Cytosine (C)
• Guanine (G)

The bases of the DNA pair with each other to form the double helix. Each DNA double helix has about 3 billion base pairs. When stretched out, it would be equivalent to 6 feet.