Cloning, a term popularized by the birth of Dolly the Sheep in 1997, refers to the process of creating an exact genetic copy of an organism. While Dolly’s arrival brought cloning into the public consciousness, the underlying technologies had been developing for quite some time. This article delves into the methods used to create clones in a lab, focusing on artificial embryo twinning and somatic cell nuclear transfer.
1. Artificial Embryo Twinning: Mimicking Nature’s Twins
Artificial embryo twinning is a relatively simple technique that mimics the natural process by which identical twins are formed.
Alt: Artificial embryo twinning process illustrating the separation of an early embryo into individual cells in a petri dish before being implanted into a surrogate mother.
In nature, identical twins arise when a very early embryo splits into two. This division occurs in the initial days following fertilization, when the embryo consists of a small cluster of unspecialized cells. Each half of the embryo then continues to divide and develop independently, ultimately leading to the formation of two separate, genetically identical individuals.
Artificial embryo twinning replicates this process outside the body. A very early embryo is separated into individual cells within a Petri dish. These cells are allowed to divide and develop for a short period. The resulting embryos are then implanted into a surrogate mother, where they complete their development. Because all the embryos originated from the same fertilized egg, they are genetically identical clones.
2. Somatic Cell Nuclear Transfer: Cloning Dolly the Sheep
Somatic cell nuclear transfer (SCNT), also known as nuclear transfer, employs a different strategy compared to artificial embryo twinning, but it achieves the same outcome: the creation of an exact genetic copy, or clone, of an individual. This was the technique that produced Dolly the Sheep, a landmark achievement in cloning history.
Let’s break down the term SCNT to understand the process:
Somatic cell: A somatic cell is any cell in the body that is not a sperm or egg cell (reproductive cells), also known as germ cells. In mammals, somatic cells contain two complete sets of chromosomes, whereas germ cells contain only one.
Nuclear: The nucleus is a specialized compartment within a cell that houses the cell’s DNA. The DNA is organized into structures called chromosomes, which carry all the genetic information necessary to create an organism. Subtle variations in our DNA contribute to our individual uniqueness.
Transfer: The act of moving an object from one location to another.
The SCNT process involves several key steps. Researchers first isolate a somatic cell from an adult female sheep. Next, they remove the nucleus, containing all of its DNA, from an egg cell. Then, they transfer the nucleus from the somatic cell into the enucleated (nucleus-removed) egg cell.
Alt: Somatic cell nuclear transfer diagram showing the transfer of a somatic cell nucleus into an enucleated egg cell, leading to the creation of a cloned embryo.
Following a few chemical adjustments, the egg cell, now containing the somatic cell’s nucleus, begins to behave like a freshly fertilized egg. It develops into an embryo, which is then implanted into a surrogate mother and carried to term. (The transfer step often involves using an electrical current to fuse the membranes of the egg cell and the somatic cell.)
The resulting lamb, Dolly, was a precise genetic replica of the adult female sheep that donated the somatic cell. She was the first mammal ever successfully cloned from an adult somatic cell, marking a significant breakthrough in the field of cloning.
In conclusion, while different in their approach, both artificial embryo twinning and somatic cell nuclear transfer achieve the same goal: creating a genetically identical copy of an organism, furthering our understanding and application of cloning technologies.
