Center for Jewish Genetic Diseases
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Resources: Glossary
amniocentesis - procedure used for prenatal diagnosis, which involves insertion of a needle through the abdomen into the amniotic fluid. This procedure is performed using ultrasound guidance, and allows the physician to obtain a small amount of amniotic fluid which can then be used for testing. Amniocentesis is usually performed between 15 and 18 weeks of pregnancy. chorionic villus sampling (CVS) - procedure used for prenatal diagnosis, which involves insertion of a needle through the abdomen into fingerlike projections of the placenta which are called chorionic villi. This procedure is also performed using ultrasound guidance, and testing can be performed with the tissue obtained. Depending upon the location of the placenta, the tissue may be obtained transvaginally rather than abdominally, by inserting a catheter through the cervix and into the uterus, or transabdominally, with a fine needle. CVS is usually performed at 10 to 12 weeks of pregnancy. chromosome - structures found in the nucleus of the cell, which are visible under a microscope and which contain genetic (inherited) information. Human cells contain 46 chromosomes, which come in pairs. There are twenty-two pairs of chromosomes, which are referred to as autosomes, because they do not determine the sex of an individual. The twenty-third pair are referred to as the sex chromosomes, and are called the X and Y chromosomes. A woman has two X chromosomes, and a man has one X and one Y chromosome. Each chromosome contains thousands of individual genes, which will in turn determine an individual’s characteristics. cytogenetics - the study of human chromosomes. deoxyribonucleic acid (DNA) - the chemical sequence found in genes, and which allows for the transmission of inherited information from generation to generation. dominant inheritance - a pattern of inheritance whereby a single gene mutation may lead to a specific genetic disease. Children of an individual affected with a dominantly inherited condition (often referred to as autosomal dominant if the gene is not located on the X or Y chromosomes) have a 50% chance to inherit the gene mutation. enzyme - a substance that in small amounts increases the rate of a specific biochemical reaction. Often enzymes are required for the normal metabolism, or breakdown, of substances in the body. gene - often referred to as the "unit of heredity," a gene is composed of a sequence of DNA required to produce a functional protein. mutation - a change in the sequence of DNA. Many mutations are "silent" and do not cause disease. When mutations occur in genes and disrupt the production of a functional protein, they may lead to genetic disease. recessive inheritance - pattern of inheritance whereby disease results only when an individual inherits two gene mutations for the particular disease. The parents of a child who is affected are said to be "carriers" of the disease, because they have one mutation and do not manifest symptoms. If both members of a couple are carriers, there is a 1 in 4 or 25% chance in each pregnancy for a child to be affected. Also referred to as autosomal recessive inheritance if the gene is not located on the X or Y chromosomes. National Human Genome Research Institute (NHGRI) Glossary of Genetic Terms Department of Energy's Oak Ridge National Laboratory Genome Glossary Discovery Health Channel Family Genetics Glossary Glossarist.com Genetics Glossaries and Genetics Dictionaries |
elow you will find words commonly referenced on this Web site. If you scroll to the bottom, you will find links to more comprehensive online glossaries and dictionaries of Genetics terms.