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GENES AND THE GENETIC CODE

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  P265-266

2026-08-13

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GENES AND THE GENETIC CODE

There are billions of base pairs within the 46 chromosomes. Certain sections of these base pairs have special functions in inheritance and the development of an embryo after conception. These sections of chromosomes are called genes. The ordering of the base pairs in genes provides the chemical instructions to manufacture particular proteins. These genetic instructions are copied onto RNA (ribonucleic acid) that transmits this information to protein manufacturing sites in the cell. Each gene provides instructions for building a particular protein. Virtually all human characteristics (and those of other animals) are defined and controlled by genes. Sometimes a single gene determines a trait as in the case of certain blood types such as ABO (this describes the presence of A or B antigens on red blood cells). In the case of some other characteristics such as hair color or eye color, several genes, acting in concert, determine the characteristics of the trait. At one time there were estimated to be up to 100,000 genes in a human being. Since the “Human Genome Project” was completed, it has been determined that there are only about 30,000 protein coding genes. It has also been shown by the Genome Project, however, that these 30,000+ genes are able to manufacture between 100,000 and 1 million proteins. The Human Genome Project has been a global effort to map the entire human genome. The ultimate goal of this project is to find all genes on all chromosomes and determine their functions.

FIGURE 1 The human genome contained in every cell consists of 23 pairs of chromosomes and a small circular genome known as mitochondrial DNA. Chromosomes 1–22 are numbered according to their relative size and occur in single copy pairs within a cell’s nucleus with one copy being inherited from one’s mother and the other copy coming from one’s father. Sex chromosomes are either X,Y for males or X,X for females. Mitochondrial DNA is inherited only from one’s mother and is located in the mitochondria with hundreds of copies per cell. Together the nuclear DNA material amounts to over 3 billion base pairs (bp) while mitochondrial DNA is only about 16,569 bp in length.