A new technique enables the determination of the sex of cattle and goats at the embryonic stage
INDIAN scientists have developed a method to determine the sex of farm animal embryos before they are implanted in surrogate mothers. Recently, some calves whose sex was known at the embryonic stage were born at the Shree Nasik Panchawati Panjrapol (SNPP) -- a regional centre of the Anand-based National Dairy Development Board -- in Nasik and goats from embryos of predetermined sex are next in line.
The feat was achieved by a team of scientists headed by Sandeep Basu, the director of the Delhi-based National Institute of Immunology (NII) and comprising S M Totey, K B C Appa Rao, M Taneja and C H Pawashe of the NII and Suresh Gangawane, V R Dharmadhikari and A J Inamdar of the Nasik-based SNPP.
The new method opens up possibilities for establishing embryo repositories or banks where embryos of predetermined sex can be preserved in liquid nitrogen for years and can be taken when required. Moreover, as there is a paucity of male animals with known pedigree, this technique could be used to ensure that high quality male embryos are available in breeding centres and sperm stations.
To sex embryos, the scientists have exploited genetic engineering techniques. They identified a part of the deoxyribonucleic acid (DNA) -- the chemical that carries the genetic code -- from the Y chromosome which is present only in male animals. Then, they synthesised in the laboratory artificial DNA segments with the same sequences as that of the DNA part identified earlier.
Using these synthesised DNA sequences and a technique known as the polymerase chain reaction (PCR), which is used to make copies of particular parts of the DNA, the scientists can sex the embryo. The embryo cells were obtained through a biopsy technique developed by the NII scientists. With this technique, 2 to 3 cells from the embryo were removed, using microscopic tools, without damaging the rest of the embryo. The DNA from the isolated embryonic cells was then amplified using the PCR technique, and its sex determined. The test takes about 5 hours.
After pre-determining the sex, the biopsised embryos were individually transplanted into synchronised recipient mothers. The synthetic DNA obtained from the bovine Y chromosome is also used to determine the sex of goat and buffalo embryos because all of them belong to the same family and share the chosen DNA sequences.
---(S M Totey works for the Delhi-based National Institute of Immunology.).
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