The DNA in a person is a combination of the DNA from each of their parents. Part of an organism's DNA is non-coding DNA sequences. They do not code for protein sequences.
The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides. Each nucleotide is composed of a nitrogen-containing nucleobase —either cytosine (C), guanine (G), adenine (A), or thymine (T)—as well as a monosaccharide sugar called deoxyribose and a phosphate group. Deoxyribonucleic acid (/diˌɒksiˌraɪbɵ.njuːˌkleɪ.ɨk ˈaesɪd/ ; ˈæSɪD) dna is a molecule that carries most of the genetic instructions used in the, development functioning and reproduction of all known living organisms and many. viruses There are four kinds of nucleotides in a DNA molecule: cytosine, guanine, adenine, and thymine—C, G, A, and T, for short. Specific sequences of these bases, known as genes, form codes that contain all of an organism's genetic information.  Basic structure of DNA showing spiral backbone and different nucleotides (Forluvoft via Wikimedia Commons). DNA itself is made up of smaller molecules called nucleotides that link up together to form two chains that are twisted together, a bit like the separate strands of a rope. But this twisted chain is not physically used to make, or build anything else other than more molecules of DNA. A flat layer of cells forms human skin and a layer of cells folded to form a tube is how things like intestines or windpipes are formed. Cells, not DNA, are what act as building blocks. So, starting with DNA and finishing with a human: Genes are made of DNA. This is a very simple definition of DNA and how it’s arranged to form a gene, but it doesn’t tell you what a gene does, or what it’s for, or how it relates to the colour of your hair or your height or what causes some types of disease. A flat layer of cells forms human skin and a layer of cells folded to form a tube is how things like intestines or windpipes are formed. Cells, not DNA, are what act as building blocks. So, starting with DNA and finishing with a human: Genes are made of DNA. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder. An important property of DNA is that it can replicate, or make copies of itself. DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone. DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA) The DNA in a person is a combination of the DNA from each of their parents. Part of an organism's DNA is  non-coding DNA  sequences. They do not code for protein sequences. Some noncoding DNA is transcribed into non-coding RNA molecules, such as transfer RNA, ribosomal RNA, and regulatory RNAs).  DNA structure. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA's instructions, or genetic code. Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children. After the analysis of these AIMs, in a sample of a person's DNA, the likelihood (or probability) that a person is derived from any of the parental populations and any of the possible mixes of parental populations is calculated.  Single nucleotide polymorphisms, frequently called SNPs (pronounced “snips”), are the most common type of genetic variation among people. Each SNP represents a difference in a single DNA building block, called a nucleotide. For example, a SNP may replace the nucleotide cytosine (C) with the nucleotide thymine (T) in a certain stretch of DNA. SNPs occur normally throughout a person’s DNA. They occur once in every 300 nucleotides on average, which means there are roughly 10 million SNPs in the human genome. Most commonly, these variations are found in the DNA between genes. 
https://en.wikipedia.org/wiki/DNA http://www.thefreedictionary.com/DNA https://purpletriceratops.wordpress.com/2014/01/08/how-does-dna-make-a-person/ https://purpletriceratops.wordpress.com/2014/01/08/how-does-dna-make-a-person/ http://ghr.nlm.nih.gov/handbook/basics/dna https://simple.wikipedia.org/wiki/DNA http://www.livescience.com/37247-dna.html http://www.ancestrybydna.com/ancestry-by-dna-faq.php http://ghr.nlm.nih.gov/handbook/genomicresearch/snp
how dna defines a person