Cloning represents a scientific process involving the creation of a genetically identical copy of a biological entity. This entity can range from a single gene to a cell or even an entire organism. The technique produces duplicates with the exact genetic makeup of the original.
Understanding Different Cloning Processes
The field of cloning encompasses several distinct methodologies, each serving a unique purpose in biological research and potential applications. Reproductive cloning, for instance, aims to generate a complete organism that is a genetic duplicate of another existing organism.
In contrast, therapeutic cloning focuses on producing embryonic stem cells for research or medical treatments. The goal is not to create a new organism, but rather to derive specialized cells that can potentially be used to repair or replace damaged tissues. These cells are genetically matched to the donor.
Gene cloning, also known as molecular cloning, operates at a much smaller scale. Its objective is to create multiple identical copies of a specific gene or DNA segment.
Steps in Reproductive Cloning
Reproductive cloning, exemplified by the creation of Dolly the sheep, typically involves a technique known as Somatic Cell Nuclear Transfer (SCNT). The process begins with obtaining a somatic cell, which is any cell from the body other than a sperm or egg cell, from the animal to be cloned.
Concurrently, an unfertilized egg cell is retrieved from a different donor. The nucleus, which contains the genetic material of this egg cell, is carefully removed in a process called enucleation. This creates an enucleated egg cell, ready to receive new genetic instructions.
The nucleus from the donor somatic cell is then transferred into the enucleated egg cell. Following this transfer, the reconstructed egg cell is stimulated, often with an electrical pulse, to activate its development. This prompts the cell to begin dividing and forming an embryo.
As the embryo develops to an early stage, typically a blastocyst, it is then implanted into the uterus of a surrogate mother. The surrogate carries the pregnancy to term, and if successful, the result is an offspring that is a genetic replica of the somatic cell donor.
Steps in Therapeutic Cloning
Therapeutic cloning also utilizes the Somatic Cell Nuclear Transfer (SCNT) technique, sharing several initial steps with reproductive cloning. The process starts with isolating a somatic cell from a patient or donor, which provides the genetic material for the clone. Simultaneously, an unfertilized egg cell is obtained from which the nucleus is carefully removed.
The nucleus from the donor somatic cell is then transferred into the enucleated egg cell. This reconstructed egg cell is subsequently activated, often through electrical stimulation, to initiate cell division and embryonic development. These initial stages are identical to those in reproductive cloning, aiming to create an early-stage embryo.
The significant divergence in therapeutic cloning occurs after the embryo begins to develop. Instead of implanting the embryo into a surrogate mother, the embryo is allowed to grow in a laboratory dish for approximately five to seven days. During this period, it reaches the blastocyst stage.
At the blastocyst stage, the inner cell mass, which contains pluripotent embryonic stem cells, is carefully isolated. These stem cells are then cultured in vitro, meaning they are grown in a controlled laboratory environment. The goal is to generate these genetically matched stem cells, which can be differentiated into various specialized cell types for research or potential therapeutic applications, rather than creating a complete organism.
Steps in Gene Cloning
Gene cloning, distinct from organismal cloning, focuses on making multiple identical copies of a specific DNA segment. The initial step involves isolating the target gene from the organism’s DNA, often using specific enzymes that cut DNA at precise locations.
Once isolated, the gene is inserted into a small, circular piece of DNA known as a plasmid, which serves as a vector. Plasmids naturally occur in bacteria and can replicate independently. The gene is ligated, or “glued,” into the plasmid using enzymes, creating a recombinant DNA molecule.
This recombinant plasmid is then introduced into a host bacterium, typically Escherichia coli, through a process called transformation. The bacteria are treated to make their cell membranes permeable, allowing them to take up the foreign plasmid.
As the host bacteria multiply through cell division, they replicate the plasmid along with their own DNA. This results in a large population of bacteria, each carrying multiple copies of the desired gene.