A cell is the smallest unit of living structure capable of independent existence. Cells are the basic building blocks of living things.
Every cell contains protein. The major part of organs, skin and muscles is protein. All body fluids, except bile and urine, contain protein.
Deoxyribonucleic acid (contained in all cells) is the material that holds genes.
A gene is a short piece of DNA, which tells the body how to build a specific protein. Each protein has unique functions. Proteins are the basis of body structures such as skin and hair.
The gene is the basic physical unit of inheritance. Genes pass from parents to offspring and contain the information needed to specify traits.
These genes (or short pieces of DNA) are on structures called chromosomes. Humans have approximately 20,000 genes on their chromosomes, arranged one after another.
A chromosome contains a single, long deoxyribonucleic acid molecule. The main role of deoxyribonucleic acid molecules is to store information. This information provides the complete instructions (genome) needed to build and maintain the variety of cells in your body.
Every person has 23 pairs of chromosomes.
Everyone inherits one of each pair from their mother and the other from their father.
The sex chromosomes form one of the 23 pairs of human chromosomes in each cell.
The other 22 pairs are autosomal. (An autosomal is simply a chromosome that is not a sex chromosome.)
The Sex Chromosome and DNA Testing
There are many types of genetic testing. Generally, testing falls within several broad categories. There is genetic testing for diagnostic purposes; and, to identify gene disorders and mutations. Then, there is testing for forensic purposes associated with crime, a crime suspect, or identifying victims of catastrophes.
Genetic testing associated with genealogy research is concerned with identifying biological relationships between people.
Normally, every person has one pair of sex chromosomes in each cell. Males have one X and one Y chromosome. Females have two X chromosomes. The mother always contributes an X chromosome to the child. The father may contribute an X or a Y. Thus, the chromosome from the father determines the gender of the child.
Only males possess the Y-chromosome.
The Y chromosome passes largely unchanged from father to son.
Researchers discovered a novel mechanism by which the Y chromosome maintains its genetic integrity. That mechanism gives it the ability to edit out genetic mistakes and maintain the integrity of the genes it carries.
Consequently, the paternal lineage test can go back dozens of generations into the past. Through DNA testing, you could find (present day) cousins many generations removed from your common ancestor.
See the web page on Genealogical Test for additional information.
Genetics Home Reference – A service of the U.S. National Library of Medicine
A PDF Guide to Your Genome - National Human Genome Research Institute
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