Genetically modified animal
The vast majority of genetically modified animals are at the research stage while the number close to entering the market remains small.
With animals DNA is generally inserted into using microinjection, where it can be injected through the cell's nuclear envelope directly into the nucleus, or through the use of viral vectors.
Then researchers would have to wait until the animal reached breeding age and then offspring would be screened for presence of the gene in every cell, using PCR, Southern hybridization, and DNA sequencing.
[30] The first genetically modified animal to be commercialised was the GloFish, a Zebra fish with a fluorescent gene added that allows it to glow in the dark under ultraviolet light.
[37][49] Livestock are modified with the intention of improving economically important traits such as growth-rate, quality of meat, milk composition, disease resistance and survival.
[54][55] The A transgene construct consisting of a promoter expressed in the murine parotid gland and the Escherichia coli phytase gene was introduced into the pig embryo by pronuclear microinjection.
However the Dutch Agriculture Minister at the time, Jozias van Aartsen, granted him a reprieve provided he did not have more offspring after public and scientists rallied to his defence.
They say that he represents the start of a new era in the way man deals with nature, an icon of scientific progress, and the subsequent public discussion of these issues.
[64] Researchers have developed GM dairy cattle to grow without horns (sometimes referred to as "polled") which can cause injuries to farmers and other animals.
DNA was taken from the genome of Red Angus cattle, which is known to suppress horn growth, and inserted into cells taken from an elite Holstein bull called "Randy".
[79] Genetic modification of the myxoma virus has been proposed to conserve European wild rabbits in the Iberian peninsula and to help regulate them in Australia.
[98][99] In November 2018, He Jiankui announced that he had edited the genomes of two human embryos, to attempt to disable the CCR5 gene, which codes for a receptor that HIV uses to enter cells.
He said that twin girls- Lulu and Nana, had been born a few weeks earlier, and that they carried functional copies of CCR5 along with disabled CCR5 (mosaicism), and were still vulnerable to HIV.
It was originally developed by one of the groups to detect pollution, but is now part of the ornamental fish trade, becoming the first genetically modified animal to become publicly available as a pet when it was introduced for sale in 2003.
Two species of fish- zebrafish and medaka, are most commonly modified, because they have optically clear chorions (membranes in the egg), rapidly develop, and the 1-cell embryo is easy to see and microinject with transgenic DNA.
[108][109] The generation of transgenic protocols (whole organism, cell or tissue specific, tagged with reporter genes) has increased the level of information gained by studying these fish.
[115][121] In biological research, transgenic fruit flies (Drosophila melanogaster) are model organisms used to study the effects of genetic changes on development.
[124] Transposons (particularly P elements) are well developed in Drosophila and provided an early method to add transgenes to their genome, although this has been taken over by more modern gene-editing techniques.
[129][130] In trials the populations of Aedes aegypti mosquitoes, the single most important carrier of dengue fever and Zika virus, were reduced by between 80% and by 90%.
[136] A strain of pink bollworm that were sterilised with radiation were genetically engineered to express a red fluorescent protein making it easier for researchers to monitor them.
This includes studying embryo development,[143] preventing the transmission of bird flu[144] and providing evolutionary insights using reverse engineering to recreate dinosaur-like phenotypes.
[147] A team of geneticists led by University of Montana paleontologist Jack Horner is seeking to modify a chicken to express several features present in ancestral maniraptorans but absent in modern birds, such as teeth and a long tail,[148] creating what has been dubbed a 'chickenosaurus'.
The European Union's Director General for Health and Food Safety has confirmed that made in this way eggs can be marketed,[153] although none are commercially available as of June 2023.
[162][161] The wound-healing abilities of amphibians have many practical applications and can potentially provide a foundation for scar-free repair in human plastic surgery, such as treating the skin of burn patients.
[166] Current methods of freezing and thawing axolotl sperm render them nonfunctional, meaning transgenic lines must be maintained in a facility and this can get quite costly.
Transgenes can also be combined with RNAi to rescue phenotypes, altered to study gene function, imaged in real time as the cells develop or used to control expression for different tissues or developmental stages.
The technology also opens the way to investigate the genes responsible for some of the cucumbers more unusual traits, including hibernating in summer, eviscerating their intestines, and dissolving their bodies upon death.
[189] Cnidaria such as Hydra and the sea anemone Nematostella vectensis are attractive model organisms to study the evolution of immunity and certain developmental processes.
Nonetheless, the on-going discussion about GM crops [1], and the developing debate about the safety and ethics of foods and pharmaceutical products produced by both GM animals and plants, have provoked varying views across different sectors of society[195] Genetic modification and genome editing hold potential for the future, but decisions regarding the use of these technologies must be based not only on what is possible, but also on what is ethically reasonable.
This has led ethical committees to adopt the principles of the four Rs (Reduction, Refinement, Replacement, and Responsibility) as a guide for decision-making regarding animal experimentation.
