Biotechnology has also contributed in the field of genetic counseling especially to the couples who may be at high risk of giving birth to a child with congenital defects or diseases. These parents can decide voluntarily not to have a child or may undergo selective abortions after investigations during antenatal care.
The hereditary or congenital defects are tested through the process of amniocentesis. Around the fifteen week of pregnancy, a sample of amniotic fluid containing fetal cells is removed and cultured in vitro. The cultured cells are then subjected to biochemical enzyme test and karyotype analysis. The results are particularly relevant to the situation where one or both parents have a family history of a particular hereditary disease and one has to evaluate the possible chances of the children having the same disease.
This type of test followed by genetic counseling is also done when a couple may have an abnormal child and would like to know the chances of having abnormal child on the next pregnancy. In some cases, if the defect is controlled by single recessive gene and both parents are normal, in three out of four cases the child would be normal. At least 35 diseases which can be identified by this technique are known. The number of disease specific DNA probes is also increasing at a fast rate, so that antenatal diagnosis by DNA analysis or ‘enzyme linked immunosorbent assay’(ELISA) should be possible for all single gene defects e.g. the incidence of Thallassemia in Cypriot community in U.K. has decreased to 20 per year following the use of antenatal diagnosis.
Making a choice of baby's sex
It is always interesting for a married couple to know the sex of the unborn baby. The chromosome techniques have made it possible to know the sex of the developing fetus by drawing amniotic fluid and preparing karyotypes from cells derived from the fetus which are floating in this fluid.
Using certain procedures it has been possible to have a child of a preferred sex. The technique involves “sephadex gel column” in which sperms with Y chromosome are trapped in the gel as they are lighter and the X bearing sperms reach the bottom as they are heavier. After separation these sperms are used to fertilize the ova by artificial insemination.