Biology 101
DNA is found in every cell in your body except the red blood cell. It is located in the center of the cell in a membrane called the nucleus. DNA contains all the information necessary to coordinate the functions of your body from wiggling your toes to operating your heart. That’s a lot of information! A typical animal cell contains one meter of DNA. Written
in a linear alphabet of four letters, the genetic information carried in a human cell could fill a book of more than 500,000 pages! How is that much information packaged? DNA is tightly wrapped in configurations known as chromosomes.
Genes are the functional units of DNA. They are the part of the DNA that provide the instructions for life. The human genome is estimated to contain 30,000 to 40,000 genes.
Click here to see other images and explanations of the cell, cell structures and DNA.
Only about 2% of the human genome contains genes; the remainder consists of noncoding regions, whose functions vary from giving structure to the chromosome, to having no detectable purpose. These segments of “junk DNA” as they are sometimes called, are useful for genealogical purposes. (Please see Biology 201 for further explanation.)
Humans have a total of 46 chromosomes, which are grouped into pairs. Each of the 23 pairs consist of one chromosome from our mother and one from our father. In females the 23rd chromosome pair consists of two X chromosomes. Males, however, have an X chromosome and a Y chromosome. Therefore, It is the Y chromosome (Ycs) that determines the male gender. It is also the Y chromosome (Ycs) that is one of the most useful chromosomes in genealogical studies. The Y chromosome has the unique property of being passed virtually unchanged from generation to generation. This means that a man and all his sons will have the same, or similar, Y chromosome. Likewise, he will have the same Y chromosome as his father and grandfather and so on. This gives the Y chromosome the unique property of following the surname, in most cases, which makes it a very valuable genealogical tool.
The DNA found in the nucleus of the cell is often referred to as the nuclear or autosomal DNA. DNA can also be found in the mitochondria of the cell. The mitochondria is the power house of the cell. It is responsible for producing energy to perform all the cellular functions. The mitochondrial DNA (mtDNA) follows the direct maternal line. Women pass their mtDNA to all of their children, but then only the daughters will pass it on to the next generation (as seen in the chart to the right).
For more information about genetics, laboratory techniques and cell biology visit the National Center for Biotechnology Information.
