Hardly a day goes by without something in the newspaper, radio, or TV about genetics and the great strides in molecular understanding of the human genome, i.e. our entire complement of genetic material. And now hardly a week goes by without something appearing about what the understanding of our genomes is telling us about human evolutionary, ethnic, and migrational history. Now, I would say that hardly a month goes by without some major article or program appearing on the role of genetics in genealogical research. A recent good one is called "Tracing Your Genetic Roots," which appeared in U.S. News & World Report, Jan. 29, 2001, pages 34-41. (Also found at the U.S. News Web site, http://www.usnews.com/usnews/issue/010129/migration.htm) The frequencies of these appearances will certainly accelerate, as all our knowledge is accelerating today.

The objective of this article is to outline this relatively new interdependence of genealogy and genetics. Please bear with me while I provide just a few simple definitions that I hope will make the following discussion clearer:

DNA: An abbreviation for deoxyribose nucleic acid, four varieties of which make up the complete molecular code for our genes. Most of us are more than 99 percent identical in our DNA make-up. It is the fraction of a percent variation among us that along with environmental differences, makes us differ from one another. 

Genes: molecules comprised of thousands of nucleic acids. Our genomes are estimated to contain 40,000 to 70,000 genes. 

Polymorphisms, literally meaning "many forms," are the often seen variations in DNA structure that are not usually associated with genetic disease. These relatively neutral small variants, because they are scattered throughout the genome, can be used to locate genes to specific chromosomes and furthermore position those genes quite precisely on the chromosome. 

Genomes are the complete complement of our molecularly organized genes as well as a large fraction of other DNA whose function is not clear. 

Chromosomes are the paired tiny bodies of long segments of DNA contained within the nucleus of each cell. In humans there are 23 pairs of chromosomes. Each of us inherits one of each pair from one parent and one of each pair from the other parent. 

Nucleus of the cell. Inside each cell of our body, except the red blood cells, is a roughly spherical nucleus that contains all 23 pairs of chromosomes. 

Cells are the tiny living compartments in all our tissues, the fundamental building blocks of our bodies. There are billions of them. 

X-linked recessive condition is a trait that is located on the X chromosome one of the sex chromosomal pair. A female has two X chromosomes. If there were a recessive mutation on one of them, the normal dominant variant on the other would cover up the condition and usually make its manifestation much less severe or absent. But the male has an X and a Y, the Y a tiny chromosome lacking the vast majority of genes on its paired X chromosome. So when an X chromosome with a recessive variant on it is paired in the male with the Y chromosome, the mutated variant is exposed without a covering normal gene, and the disease is expressed. That is why X-linked conditions are predominantly seen in males rather than females.

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