A genetic disease is a disease caused by a gene that is not normal. A genetic mutation is a gene that has not been copied correctly during cell division and has a different sequence or shape than other genes in the body. If you have a genetic mutation, your body cannot develop normal form and function. Watson and Crick suggested that DNA consists of two strands twisted around each other to form a right-handed helix called a double helix. The basic pairing takes place between a purine and a pyrimidine: namely the A pairs with T and the G pairs with C. In other words, adenine and thymine are complementary base pairs, and cytosine and guanine are also complementary base pairs. This is the basis of Chargaff`s reign; Because of their complementarity, there is as much adenine as thymine in a DNA molecule and as much guanine as cytosine. Adenine and thymine are connected by two hydrogen bonds, and cytosine and guanine are connected by three hydrogen bonds. Both components are anti-parallel in nature; That is, one strand has the 3` carbon of sugar in the „high” position, while the other strand has the 5` carbon in the ascending position. The diameter of the DNA double helix is uniform everywhere, because a purine (two rings) always associates with a pyrimidine (one ring) and their combined lengths are always the same. (Figure 9.4). Because DNA is hereditary, DNA testing is often used in legal cases to determine maternity or paternity — for example, when custody and child support are at stake. As the UK`s National Health Service explains, scientists can compare two people`s DNA with a blood test or even a salivary swab from the inside of the cheek.

DNA tests can even be done before a child is born, using tissue from the placenta or a sample of amniotic fluid surrounding the child in the womb. This type of test can also be used to look for genetic abnormalities that indicate disease and disease. DNA is made up of chemical building blocks called nucleotides. These building blocks consist of three parts: a phosphate group, a sugar group, and one of four types of nitrogenous bases. To form a strand of DNA, nucleotides are linked in chains, alternating phosphate and sugar groups. The four types of nitrogenous bases present in nucleotides are: adenine (A), thymine (T), guanine (G) and cytosine (C). The order or sequence of these bases determines which biological instructions are contained in a strand of DNA. For example, the sequence could instruct ATCGTT for blue eyes, while ATCGCT could instruct for brown eyes. The complete DNA textbook or a human`s genome contains about 3 billion bases and about 20,000 genes on 23 pairs of chromosomes. Genes are the building blocks of your body. Some genes give instructions for making proteins. The job of a protein is to tell your body what kinds of physical characteristics you should have, like the color of your hair and eyes.

Some genes code for RNA to perform other tasks. Biologists in the 1940s had a hard time accepting DNA as genetic material because their chemistry was seemingly simple. DNA was known to be a long polymer composed of only four types of chemically similar subunits. In the early 1950s, DNA was first studied using X-ray diffraction analysis, a technique for determining the three-dimensional atomic structure of a molecule (see Chapter 8). Early X-ray diffraction results showed that DNA consisted of two polymer strands wrapped in a helix. The observation that DNA was double-stranded was crucial and provided one of the most important clues that led to the Watson-Crick structure of DNA. It was only when this model was proposed that the potential of DNA for replication and coding of information became evident. In this section, we look at the structure of the DNA molecule and explain in general how it is able to store genetic information. Chromosomes are structures that look like thread and live in the nucleus (center) of cells.

A DNA molecule and a protein form a chromosome. Chromosomes vary in size, and proteins called histones allow them to pack small enough to fit inside a nucleus. Without it, our chromosomes would be as big as we are! Chromosomes give your cells the real instructions to make you unique. The phosphate group of one nucleotide covalently binds to the sugar molecule of the next nucleotide, etc., forming a long polymer of nucleotide monomers. The sugar-phosphate groups line up in a „backbone” for each strand of DNA, and the nucleotide bases protrude from this backbone. The carbon atoms of sugar with five carbon atoms are numbered clockwise by oxygen as 1′, 2′, 3′, 4′ and 5′ (1′ is read as „a prime number”). The phosphate group is bound to the 5` carbon of one nucleotide and the 3` carbon of the next nucleotide. In its natural state, each DNA molecule actually consists of two individual strands that are held together along their length by hydrogen bonds between the bases. People should have 23 pairs of chromosomes (46 in total). Chromosomes are divided into 22 numbered pairs (autosomes) and one pair of sex chromosomes (X and Y). You get one chromosome from each parent to form a pair. Such advances in the technologies and processes used to collect and analyze DNA are just part of what makes advanced DNA profiling so useful.

Another aspect is the rise of database technology. If law enforcement agencies can search for large amounts of DNA data stored in computer databases, they have a better chance of finding matches for material collected at crime scenes. This is archived content from the U.S. Department of Justice website. The information here may be out of date and the links may no longer work. Please contact webmaster@usdoj.gov if you have any questions about the archive page. In 1953, Francis Crick and James Watson described the molecular form of DNA as a „double helix.” Double-stranded DNA consists of two linear strands facing each other, called antiparallel strands; These strands twist into a double helix. The structure of DNA can also be described as a conductor. The chemical backbone of conductors consists of sugar and phosphate molecules connected by chemical bonds. The rungs of the scale are pairs of units between A and T or between C and G. These pairs are called base pairs and connect the two sugar-phosphate skeletons through interactions called hydrogen bonds. In cells, the DNA helix is often overcome, resulting in a phenomenon known as superwinding.

Currently, many of our country`s crime labs do not have the capacity to analyze DNA samples in a timely manner. Many have limited equipment resources, outdated information systems and overwhelming case management requirements. As a result, the criminal justice system as a whole is not able to take full advantage of DNA technology. The President`s initiative will provide federal funding to automate and further improve the infrastructure of federal, state and local crime labs so they can process DNA samples efficiently and cost-effectively.