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Genetic Glossary


The baby is surrounded by amniotic fluid in the womb. The fluid contains a few of the babies skin cells. A small sample of the fluid is taken with a thin needle, through the skin of the mother's abdomen (tummy or belly). The fluid is sent to a laboratory to test the unborn baby's genes or chromosomes.


These are conditions whereby a person only needs to inherit one copy with an alteration (mutation) of the gene in order to be affected by the condition, or become affected later in life. The changed gene is dominant over the normal gene.


These are conditions whereby a person has to inherit two changed copies (mutation) of the gene (a changed copy from each parent) to be affected by the condition. A person who has only one copy of the changed gene will be an unaffected carrier.


We have 23 pairs of chromosomes. Pair number 1 to 22 are called autosomes and are common between men and women. Pair number 23 is different in men (XY) and women (XX) and therefore is called sex chromosome.


Thread-like structures which can be seen under the microscope and contain the genes. The usual number of chromosomes in humans is 46. One set of 23 chromosomes we inherit from our mother and one set of 23 chromosomes we inherit from our father.


A part of the genetic material is deleted; the term can be used to describe either a missing area of a gene or a chromosome.


A change in a gene. Sometimes when a gene is changed, its information is altered so it does not work properly. This may cause a genetic condition.


Test performed during a pregnancy to test for the presence or absence of a genetic condition in the baby.