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A Brief Key to Basic Genetics
by Yael Rosenberg, RN
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Amniocentesis
A procedure used for prenatal diagnosis. The amniocenteses procedure involves the insertion of a needle through the abdomen into the amniotic sac from which a small amount of amniotic fluid is obtained. Nowadays, the amniocentesis is performed while using ultrasound as guidance. The amniotic fluid, which includes the fetus’ DNA is used for testing. Amniocentesis is usually performed between 16 and 18 weeks of pregnancy.
Cell Nucleus
Inside the cell nucleus, 6 feet of DNA are packaged into 23 pairs of chromosomes (one chromosome in each pair coming from each parent).
Chorionic Villus Sampling (CVS)
A procedure used for prenatal diagnosis. The CVS procedure involves the insertion of a needle through the abdomen into fingerlike projections of the placenta which are called chorionic villi. This procedure is also performed while using ultrasound as guidance. The chorionic villi obtained is used for DNA testing. CVS is usually performed at 10 to 12 weeks of pregnancy.
Chromosome
The structures found in the nucleus of the cell, called the chromosomes, contain genetic (inherited) information. Human cells contain 23 pairs of chromosomes, a total of 46 chromosomes. Twenty-two pairs of chromosomes are referred to as autosomes, since they do not determine the sex of an individual. The twenty-third pair are the sex chromosomes, generally referred to as the X and Y chromosomes. Each chromosome contains thousands of individual genes. These genes determine an individual’s characteristics.
Deoxyribonucleic Acid (DNA)
The DNA is the chemical sequence found in genes. These sequence allows for the transmission of inherited information from generation to generation.
Enzyme
A substance that in small amounts increases the rate of a specific biochemical reaction is called the enzyme. Enzymes are usually required for the normal metabolism, or breakdown, of substances in the body.
Gene
Each gene is a segment of double-stranded DNA that holds the recipe for making a specific molecule, usually a protein. These recipes are spelled out in varying sequences of the four chemical bases in DNA: adenine (A), thymine (T), guanine (G) and cytosine (C). The bases form interlocking pairs that can fit together in only one way: A pairs with T; G pairs with C.
Human Cell
Each of the 100 trillion cells in the human body (except blood cells contains the entire human genome--all the genetic information necessary to build a human being. This information is encoded in 6 billion base pairs, subunits of DNA. (Egg and sperm cells each have half this amount of DNA.)
Mutation
A mutation is 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.
Protein
Proteins, which are made up of amino acids, are the body's workhorses--essential components of all organs and chemical activities. Their function depends on their shapes, which are determined by the 50,000 to 100,000 genes in the cell nucleus.
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