A Brief Key to Basic
by Yael Rosenberg, RN
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.
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.
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
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
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.
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.)
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
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.