Glossary of Genetic Terminology
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Also known as trisomy 18, is a chromosomal condition that is the result of an extra copy of chromosome 18. It is a severe condition where children with the condition may have small eyes, abnormally formed ears, heart defects and severe intellectual impairment. They rarely live past one year (see Genetics Fact Sheet 30).
EGG:
The female sex cell (ovum) which carries half the
mother's chromosomes (and therefore, half the genes). In humans, this number is normally 23. The egg joins with the sperm at conception to produce an embryo.This process is called fertilisation.
A method used to study DNA. It is the process of separating DNA molecules in a gel medium according to size and electrical charge, by applying an electric current.
EMBRYO:
The product of the fusion of an egg and a sperm at conception. This term is reserved for the first eight weeks of
development.
EMBRYONIC STEM CELLS:
Primitive (undifferentiated) cells from the embryo that have the potential to mature and develop into a wide variety of specialised cell types.
EMPIRIC RISK:
A risk estimate that is given for the chance of occurrence or recurrence of a
particular condition in an individual based on the observation of other
families with that condition.
ENVIRONMENTAL FACTORS:
Factors in the environment that may have an effect on our development or
growth eg. diet, atmospheric pollutants, cigarette smoke, preservatives, X-rays
etc.
ENZYME:
A protein molecule which promotes or enables a
chemical reaction in the cells (a biochemical
reaction) to take place. These biochemical reactions include breaking down food
into the essential chemicals required by the body and breaking down toxic
by-products of our bodies. Enzymes are essential for the correct function of
the body's metabolism.
ENZYME REPLACEMENT
THERAPY:
A method of treating genetic conditions that are due to a deficiency of a
particular enzyme. Overcoming the deficiency by
providing the body with the enzyme enables the cells to function correctly and
the symptoms of the condition may be reduced or eliminated.
Making heritable changes in the way that a gene works or functions, without altering the sequence of the genetic code, or DNA. Ways in which this may be changed is via structural changes (see Genetics Fact Sheets 14 and 15).
ETHICS/ETHICAL
BEHAVIOUR:
Code of behaviour considered correct; especially that of a particular group,
profession or individual.
EUGENICS:
The practice of trying to influence human heredity by encouraging the transmission of 'desirable' characteristics and discouraging
the transmission of 'undesirable' ones.
EXON:
The part of the DNA message
that is translated into a protein.
EXPRESSED GENE:
When the coded information contained in the gene is understood by the cells to
produce a product such as a protein.
EXPRESSIVITY:
The degree to which an inherited characteristic is expressed in a person.
'Variable expressivity' refers to the variation in expression and severity of
particular characteristics or severity of a condition.