With the new genetic diagnostic technologies and therapeutic capabilities come many controversies about how they should be used. Concerns have been raised that knowledge of a person’s genetic information might be used improperly. For instance, people whose genetic characteristics make them prone to particular disorders might be denied employment or health insurance coverage.
Prenatal screening for genetic abnormalities that cause serious disorders is widely supported. However, concern exists that screening could also be used to select for traits that are desirable (for example, physical appearance and intelligence).
(See also Genes and Chromosomes.)
A clone is a group of genetically identical cells or organisms derived from a single cell or individual.
Cloning (the producing of clones) has been commonplace for many years in agriculture. A plant can be cloned by simply taking a small piece of the original plant and growing a new one from it. In plants, this is called propagation. The new plant is thus an exact genetic copy of the original one. Such propagation is also possible with simple animals such as flatworms: cut a flatworm in two, and the tail grows a new head and the head grows a new tail. However, such simple techniques do not work with higher animals, such as sheep or humans.
In the now-famous “Dolly” experiments, cells from a sheep (donor cells) were fused with unfertilized sheep eggs from another sheep (recipient cells) from which the natural genetic material was removed by microsurgery. Then the genetic material from the donor cells was transferred into the unfertilized eggs. Unlike unfertilized eggs, these laboratory-made eggs had a complete set of chromosomes and genes. Unlike eggs fertilized naturally (with sperm), the laboratory-made eggs received genetic material from only one source. The eggs then started to develop into embryos. The developing embryos were transplanted into a female sheep (the surrogate mother), where they developed naturally. One of the embryos survived, and the resulting lamb was named Dolly. As expected, Dolly was an exact genetic copy of the original sheep from which the donor cells were taken, not of the sheep that provided the eggs.
Studies suggest that cloned higher animals (and thus humans) are more likely to have serious or fatal genetic defects than normally conceived offspring. Creating a human by cloning is widely seen as unethical, is illegal in many countries, and is technically difficult. However, cloning need not only be used to create a whole organism. It can, theoretically, also be used to create a single organ. Thus, one day a person may be able to receive “spare parts” manufactured in the laboratory, using the person’s own genes.
Whether a cell used for a clone produces a specific type of tissue, a specific organ, or an entire organism depends on the potential of the cell—that is, how highly the cell has developed into a particular type of tissue. For example, certain cells called stem cells have the potential to produce a wide variety of tissue types or even possibly an entire organism. Stem cells are unique because, unlike other cells, they have not yet changed into specific types of tissues. Other cells have changed and become specialized. They can develop into only specific tissue types such as brain or lung tissue. This process of specialization is called differentiation. Stem cells have stimulated interest because of their potential to generate tissue that can replace diseased or damaged tissues. Because stem cells tend to be less differentiated, they can thus potentially replace a wide or unlimited variety of types of tissue.
Scientists are able on a limited basis to change (edit) the deoxyribonucleic acid (DNA) within a living cell. That is, they are able to remove, add, or modify a specific segment of DNA. Newer advances have allowed better control over exactly which segment of DNA is removed and where a new segment is placed. This control is important because a major goal of this process is to be able to replace an abnormal gene with a normal one, and this requires precise control. Removing the wrong piece of DNA could be dangerous or fatal.
CRISPR–Cas9 gene editing (clustered regularly interspaced short palindromic repeats–CRISPR-associated protein 9) is a newer, more efficient technique for editing the mutated DNA sequence of a gene. This technique is still in experimental stages but has been done on several human embryos.
Gene editing would particularly help people with diseases like cystic fibrosis that are caused by a single abnormal gene. Gene editing may be less helpful for disorders that are caused by many different genes. A future possibility may even be to make genetic changes that enhance healthy people, such as making them smarter, stronger, or longer living.
The main ethical concerns about gene editing are that mistakes might be made that could be dangerous to a person and difficult to correct. Also, any negative changes that affect a person's sperm or eggs could potentially be passed to future generations.