Biochemical Techniques and Instrumentation

6.2.3.3.1. Embryo cloning

Embryo cloning is known as “embryo splitting”. This technique is similar to the natural process of creating identical twins. Twins occur in nature just after fertilization of an egg cell by a sperm cell. When the fertilized egg called a zygote tries to divide into a two-celled embryo, the two cells sometimes separate and each cell continues to divide on its own and develops into a separate individual. As the two cells come from the same zygote, the resulting individuals are genetically identical.

In artificial embryo "twinning" or "splitting", this process occurs in a petri dish instead of mother's body. It involves manual separation of individual cells from an early embryo. Sperm and an egg cell are mixed together on a glass petri dish. After conception, the zygote is allowed to develop into a blastula stage, which contains a hollow mass of cells. In-vitro fertilization (IVF) is performed at this blastula stage to increase the number of available embryos. A chemical is added to the petri dish to remove the "zona pellucida" covering. This chemical also provides nutrients to the cells to promote cell division. The blastula is then divided into individual cells which are then deposited on individual dishes. The cells are then coated with an artificial zona pellucida and allowed to divide and develop into embryos. Interruption of the zygote at the two cell stage gives best results. The resulting embryos are then implanted into a surrogate mother and allowed to develop into an individual. As all the embryos come from the same zygote, the resulting individuals are genetically identical monozygotic twins.