Cloning is the act of replicating the genetic code, cell populations, and species. There are three types of cloning: molecular, reproductive and therapeutic. Molecular cloning is used to amplify sections of DNA, reproductive cloning is to create genetically similar organisms, and therapeutic cloning is to produce stem cells from embryos. Molecular cloning has four main steps: fragmentation, ligation, transfection and screening – process is used to produce populations of recombinant DNA. In fragmentation, a DNA strand is unraveled using DNA helicase and then restriction enzymes extract the target sequence. In ligation, DNA ligase adds sticky ends to the target sequence for easy attachment to plasmid DNA. In transfection, the new DNA strand is placed in a cell. Screening is to ensure that selected cells successfully accepted the inserted DNA. These cells are then cultured to produce clones of the parent recombinant DNA strand.
Reproductive cloning creates genetically identical organisms by asexual reproduction – most common usages are for plants and animals. In plants, certain species of crops are constantly being cloned for commercial process such as strains of navel oranges. Organism cloning uses Somatic Cell Nuclear Transfer (SCNT) and it is frequently carried out with cows and sheep, a notable example is Dolly. In SCNT, the nucleus of an embryo is removed and replaced with a nucleus from donor cell. The cell is then inserted into uterus of a female sheep to carry out the pregnancy, and the offspring produced is a clone. It is a highly complex process that has many ethical implications.
Therapeutic cloning is based on the production of stem cells from embryos for the study of embryogenesis and potential treatments of disease. The nucleus of the ova is removed and placed into adult cell, this act to reprogram the cell – it will divide and form a blastocyst which can be differentiated into any cell.