Читать книгу Abnormal Psychology - William J. Ray - Страница 97

Genes form the blueprint to describe what an organism is to become. Over our evolutionary history, a majority of human genes reflect little variation. This is why all humans have two eyes and one nose and one mouth. However, perhaps one fourth of all genes allow for variation. What makes things interesting is that the two genes of these pairs are usually slightly different. The technical name for the unique molecular form of the same gene is an allele. It has been estimated that of our approximately 20,000 genes, some 6,000 exist in different versions or alleles (Zimmer, 2001).

genes: the basic physical and functional unit of heredity, made up of DNA; act as instructions to make proteins

allele: the alternative molecular form of the same gene

homozygotes or homozygous: when a person has two copies of the same allele

heterozygotes or heterozygous: when a person has two different alleles at the same location

encode: to lay out the process by which a particular protein is made; this is the job of a gene

proteins: made up of amino chains from DNA, proteins do the work of the body and are involved in a variety of processes; functionally, proteins in the form of enzymes are able to make metabolic events speed up, whereas structural proteins are involved in building body parts

When a person has two copies of the same allele, they are said to be homozygotes or homozygous for that allele. If, on the other hand, they have two different alleles for a particular gene, they are said to be heterozygotes or heterozygous for those alleles. Given that the alleles that come from your mother may not result in exactly the same characteristics as those from your father, variation is possible. It is these variations that allow for the process of natural selection to have its effect.

The job of a gene is to lay out the process by which a particular protein is made. That is, each gene is able to encode a protein, influencing its production. Proteins, which do the work of the body, are involved in a variety of processes. Functionally, proteins in the form of enzymes are able to make metabolic events speed up, whereas structural proteins are involved in building body parts. Similar proteins in insects are involved in creating such structures as spider webs and butterfly wings. Proteins are diverse and complex and are found in the foods we eat as well as made by our cells from some 20 amino acids. Proteins serve as signals for changes in cell activity as illustrated by hormones. Proteins are also involved in health and disease as well as in development and aging.

Although the cells in the body carry the full set of genetic information, only a limited amount is expressed at any one time related to the function of the cell. That is to say, although a large variety of proteins could be produced at any one time, there is selectivity as to what is produced relative to internal and external conditions. Further, the location of the genes makes a difference in that cells in the brain produce different proteins from those in the muscles, or liver, or heart.

A gene is turned on (produces the protein) or turned off (does not produce the protein) relative to specific events. Just because a person has a specific gene does not mean that it will necessarily be expressed. The environment in which a person develops and lives plays an important role in gene expression. Even identical twins with the same genotype can display different phenotypes if their environmental conditions differ during their development. For example, if one was to grow up in a high mountain range and the other in a desert below sea level, important physiological differences such as lung capacity and function would be apparent. There are few factors other than blood type in terms of human processes that can be explained totally by genetic factors alone. It is equally true that few human processes can be explained totally by the environment.