In December 1993, a team of International Scientists at French Academy of Sciences, Paris developed the world's first map of human genome. For over a decade, genetic scientists have been attempting to map the genes. So far, the physical map existed only for 2% of human genome, and the present map covers about 90% of genome. To produce the map they cut human DNA into pieces and grew each piece in a yeast cell for clones. the clones were then cut into fragments and fingerprinted to detect overlapping sections. These sections were used as guides to put the pieces back together to get the map. This will help the scientists to disc over genetic diseases. In human beings there are many cases where certain genes responsible for encoding enzymes are missing which result in genetic diseases. Some of them are briefly described as under:
a) Phenylketonuria Genes: In diseased persons when phenylalanine fails to get converted into tyrosin, distrubances in metabolism result in mental retardness. It is possible to cure this disease by using recombinant DNA techniques in early period of pregnancy.
b) Urokinase Genes: Urokinase is involved in dissolution of blood clots. Urokinase has been synthesized in huge quantity by using genetically engineered bacteria with urokinase genes.
c). Thalassaemia Genes:. It is a condition in which synthesis of α and β-globin chains is reduced and the excess chains precipitate and cause haemolytic anaemia and spleen enlargement. Human globin genes have been identified and sequenced. It has been found that α and β-globin genes are closely linked. Human globin genes (cDNA) has also been developed and cloned. However, much work has to be done to cure this disease.
d). Haemophilia Genes:. Haemophilia is sex linked disease in human where blood clotting does not take place normally due to deficiency of clotting factor VIII:C. By using gene cloning technique the clotting factor VIII : C gene was cloned which expressed in mammalian cell lines and produced the protein VIII : C responsible for blood clotting.