Most scientific fields
have a specialized vocabulary. Genetics is no exception. Understanding this vocabulary is an important
first step toward understanding genetics. The list below is a brief glossary of the vocabulary of genetics,
especially those commonly used in newspapers and magazines or on radio and
TV when discussing human genetics.
Adenosine.
One of the four building blocks of DNA (a nucleotide). The “A” in the genetic code.
Allele.
One version of a particular gene.
Each human cell has two copies of each gene.
Those two copies are often different from each other because they have
slightly different orders of genetic letters.
Each copy is an allele.
Amino
acids. The building blocks of
proteins. The genetic code works by
specifying the order of amino acids in proteins. The proteins act as the functional components
of cells.
Autosome.
Any chromosome that is not a sex chromosome, for example in humans
any chromosome other than “X” or “Y”.
Carrier.
An individual who carries a allele of a gene associated with a disease. In many cases, the carrier may not actually
have the disease associated with the version of they gene they carry, even
though they may pass it on to their offspring.
Chromosome.
The physical structure found in the nucleus of cells composed of DNA
and proteins that contains a string of genes.
Humans have 46 chromosomes: two copies each of 22 autosomes and 2 sex
chromosomes – either 2 “X” chromosome in the case of females or an “X” and
a “Y” in the case of males.
Chromosome
abnormality. A chromosome that
has become damaged. The damage may
be due to a break in the linear sequence of the chromosome, a deletion of
part of the chromosome, or movement of part of a chromosome to a place where
it is not normally found, such as the end of some other chromosome.
Codon.
Three sequential nucleotides in DNA.
One codon specifies (or codes for) a single amino acid – the building
block of proteins. There are as many
codons in a gene as there are amino acids in the protein made from that gene.
Cytosine.
One of the four building blocks of DNA (a nucleotide).
The “C” in the genetic code.
Deoxyribonucleic
acid. DNA.
The chemical information molecule used by most biological systems.
It is a string of adenosine, cytosine, guanosine, and thymidine nucleotides.
Human DNA has 3 billions nucleotide bases.
Diploid.
Having two copies (alleles) of each gene.
Most human cells are diploid. Some
cells, such as human eggs and sperm, have only one copy of each gene, so those
specialized cells are haploid.
DNA
replication. The process of duplicating
the DNA to make two identical copies, one of which will be passed along to
each daughter cell when the cell divides.
Dominant.
A version of a gene that produces an effect (phenotype) even when it
occurs as only one of the two copies present in a cell.
A dominant human gene will exert its effect in half of the progeny
of a carrier.
Gamete.
Sperm and eggs. These cells
have the special property of carrying only one copy of each gene instead the
two copies that most other cells carry. These
cells contribute to the next generation and are also called “germ line” cells.
Gene.
A single trait that is passed from generation to generation. A gene corresponds to the biological information that describes
a single protein. This information
is coded in the string of nucleotide bases, A,C,T and G.
Gene
expression. Not every gene is
expressed in every cell. Expression
refers to whether the protein coded by a gene is expressed or not.
Gene
mapping. Defining the location of genes to a particular chromosome and a particular
location of the gene on a chromosome.
Gene
therapy. The use of DNA introduced
into a cell or animal to cause the expression of a particular protein, often
one that can replace a missing or defective protein that may be responsible
for a disease.
Genetic
code. Each amino acid building
block of a protein is specified by the order of nucleotides (A,C,T and G)
in the gene for that protein. Three
adjacent nucleotides, called a codon, are required to specify one amino acid.
The genetic code can be displayed in a table that translates each of
the 64 possible triplet codons into an amino acid.
There are 64 possible combinations resulting from having one of four
nucleotides in each of three possible positions in the codon (4 X 4 X 4 =
64).
Genome.
The collection of all the genes in the organism.
Also all of the DNA that carries the genes.
Guanosine.
One of the four building blocks of DNA (a nucleotide). The “G” in the genetic code.
Haploid.
Having one copy of each gene. Gametes
usually are haploid while most somatic cells have two copies of each gene
(see diploid).
Heterozygous.
Describes the situation where cells or organisms carry two different
versions (alleles) of a given gene. For
example, one of the copies of a gene may be the normal version and one a mutant.
Homozygous.
Describes the situation where both copies of a given gene are the same.
Karyotype.
A picture of the chromosomes that allows physicians or scientists to
determine if there are large abnormalities in the chromosomes.
Linkage.
Two genes that are near each other on the same chromosome are said
to be “linked”. If one gene is inherited, the probability is
high that the other one will also be inherited.
Mutation.
A change in the sequence of nucleotides of a gene.
Some changes will alter the protein so that it no longer works normally,
while other changes may have no effect.
Non-coding
DNA. DNA that does not code for
a protein. Not all DNA codes for proteins.
Some DNA between genes is needed to help the genetic machinery express
the genes. DNA also contains segments that are repeated
many times.
Nucleotide.
The chemical name of the building blocks of DNA—A,C,T and G. DNA is a string of nucleotides.
Pedigree.
A diagram that shows the pattern of inheritance of a gene in a family.
Phenotype.
A heritable genetic trait such as eye color or blood type, or an inherited
disease.
Polymorphism.
A change in the sequence of DNA associated with a large portion of
the population. Polymorphisms may
or may not be linked to specific diseases.
Protein.
The primary component of cells. A
string of linked amino acids whose order is specified by a gene. Proteins build up most of the structures in
cells and act as little machines that work together inside of cells to accomplish
most of the things cells do.
Recessive.
A gene that only produces its affect when both copies present are identical. A recessive gene trait will be passed on to
children with only a 1 in 4 chance.
Sex
chromosome. One of two chromosomes
in humans that defines sex. There are two sex chromosomes, the X and the
Y chromosome. Males have one X and
one Y chromosome, while females have two X chromosomes.
Sex-linked.
A gene that resides on one of the sex chromosomes.
Somatic
cells. Most of the cells in our
bodies. Any cell that is not a gamete
(a sperm or egg). Mutations that occur in somatic cells are not
passed on to our offspring.
Thymidine.
One of the four building blocks of DNA (a nucleotide). The “T’ in the genetic code.