In human there are hundred Genetic which are mostly produced through recessive mutation. There is no cure to any of them except for the fast emerging option of gene therapy. Their incidence can be minimized an early detection of the afeicted which are then aborted. Therefore, when a woman gets pregnant the probability of her having child suffering from genetic disorder is estimated based on the histones of her and her husbands families further investigation is carried out for a clear cuts and specific diagnosis.
Obtaining Foetal Cells. Earlier foetal cells were obtained by amniocentesis withdrawal ofamionitic fluid with the help of hypodermic syringe. But amniocentesis is applicable only 18 weeks later after the pregnancy which is rather later of abortion. Therefore, foetal cells are now obtained from biopsies of trophoblastic villi which are an external part of human embryo and later form a part of the placenta. The biopsy is performed during 6 or 8 week of pregnancy an endoscope passed through the cervix of uterus usually provide 100 mg of pure foetal DNA.
Disease Detection.
The foetal cells are used for detection of the genetic disorders in one of the following ways.
(1) Determination of karyotype of cells provides information on various syndromes produced by gross chromosomal aberrations.
(2) Most of the genetic diseases produce defective protein or no enzymes many of these proteins have been identified and some of these can be assayed. The foetal cells are used to assay the concerned enzyme activities to detect such genetic disease. Atleast 35 genetic disease can be detected by assaying activities of specific enzymes. In case of some genetic diseases, the concerned gene mutation may alter the recognition site for restriction enzyme. The RFLP produced can be detected by Southern hybridization a sequence of the concerned gene is used as probe.
(3) A more general approach utilizes oligonucleotide probes representing the sequence altered by the gene mutation causing the genetic disease. Typically set of two separate probes are used for disease one probe is complementary to the normal sequence, while the other is complementary to the mutant sequence. The probes are radio labelled and used to probe Southern blost, under appropriate condition the probes can distinguish the normal and mutant DNA samples.
Obtaining Foetal Cells. Earlier foetal cells were obtained by amniocentesis withdrawal ofamionitic fluid with the help of hypodermic syringe. But amniocentesis is applicable only 18 weeks later after the pregnancy which is rather later of abortion. Therefore, foetal cells are now obtained from biopsies of trophoblastic villi which are an external part of human embryo and later form a part of the placenta. The biopsy is performed during 6 or 8 week of pregnancy an endoscope passed through the cervix of uterus usually provide 100 mg of pure foetal DNA.
Disease Detection.
The foetal cells are used for detection of the genetic disorders in one of the following ways.
(1) Determination of karyotype of cells provides information on various syndromes produced by gross chromosomal aberrations.
(2) Most of the genetic diseases produce defective protein or no enzymes many of these proteins have been identified and some of these can be assayed. The foetal cells are used to assay the concerned enzyme activities to detect such genetic disease. Atleast 35 genetic disease can be detected by assaying activities of specific enzymes. In case of some genetic diseases, the concerned gene mutation may alter the recognition site for restriction enzyme. The RFLP produced can be detected by Southern hybridization a sequence of the concerned gene is used as probe.
(3) A more general approach utilizes oligonucleotide probes representing the sequence altered by the gene mutation causing the genetic disease. Typically set of two separate probes are used for disease one probe is complementary to the normal sequence, while the other is complementary to the mutant sequence. The probes are radio labelled and used to probe Southern blost, under appropriate condition the probes can distinguish the normal and mutant DNA samples.
