Cloning Stem Cell Research

Cloning Stem Cell Research

Introduction

Cloning is a process by which identical copies, or clones, of something are made. In biological sciences, it is concerned with making identical copies of biological material such as DNA fragments (molecular cloning), cells (cell cloning), or organisms. It is an asexual (involving only one parent) method of reproduction. (Wilmut & Highfield, 2006)

Stem cell research is often confused with cloning as both involve the use of embryonic stem cells. While reproductive and therapeutic cloning only involve the use of embryos, stem cell research involves the use of adult stems cells, stem cells from fetuses, umbilical cord blood cells, and amniotic fluid, along with embryonic stem cells, to find cures for a variety of degenerative diseases. (Snow, 2003)

There are three main types of cloning: recombinant DNA technology or DNA cloning, reproductive cloning, and therapeutic cloning. Recombinant DNA technology or DNA cloning technology has been in use since 1970s and involves isolating a defined DNA sequence and then obtaining its multiple copies in vivo (within a cell). The DNA sequence of interest is transferred from one organism to a self—replicating genetic element, for example, a bacterial plasmid (self—replicating extra chromosomal circular DNA molecules).

There are four steps involved in DNA cloning, namely, fragmentation, ligation, transfection and screening/selection (Caplan & McGee, 2006). In fragmentation, restrictive enzymes are used to isolate the required DNA sequence from chromosomal DNA. In the second step, ligation, the plasmid that serves as a vector and is originally circular is first linearized using restrictive enzymes and then the DNA fragment of interest is inserted into it by incubating them with an enzyme called ligase. In the next step the vector containing the DNA of interest is transfected into the host cells. Mostly bacteria, yeast cells or mammal cells are used as hosts. The transfected cells are then grown in culture. In the process of selection, only cells transfected are allowed to grow; this is done by antibiotic resistance marker or color selection markers on permissive media.

Reproductive cloning involves unicellular as well as multicellular cloning. In unicellular cloning a population of cells is derived from a single cell. In organism cloning a genetically identical copy of an organism is produced. This type of cloning involves a process called somatic cell nuclear transfer (SCNT) in which the nucleus containing the genetic material of the donor's somatic cell (e.g., skin cell) is removed and placed in an egg whose nucleus has already been removed. The reconstructed egg is first given some time for the nucleus and the cytoplasm to adapt to each other, and then it is stimulated, either chemically or electrically, for division. The developing embryo is then implanted into the uterus of a host female where it completes development until birth (Snow, 2003). This type of cloning has a very low success rate.

Animal Cloning

The first organism ever to be cloned was a tadpole in 1952, but many scientists questioned if the cloning had actually occurred and experiments conducted by other labs were not able to give ...