Genetically modified mammals are

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s that have been genetically engineered. They are an important category of

genetically modified organism A genetically modified organism (GMO) is any organism whose genetic material has been altered using genetic engineering techniques. The exact definition of a genetically modified organism and what constitutes genetic engineering varies, with ...

s. The majority of research involving genetically modified mammals involves mice with attempts to produce knockout animals in other mammalian species limited by the inability to derive and stably culture

embryonic stem cells Embryonic stem cells (ESCs) are Cell potency#Pluripotency, pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage pre-Implantation (human embryo), implantation embryo. Human embryos reach the blastocyst stage 4� ...

Usage

The majority of genetically modified mammals are used in research to investigate changes in

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

when specific genes are altered. This can be used to discover the function of an unknown gene, any genetic interactions that occur or where the gene is expressed. Genetic modification can also produce mammals that are susceptible to certain compounds or stresses for testing in biomedical research. Some genetically modified mammals are used as

models A model is an informative representation of an object, person, or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin , . Models can be divided int ...

of human diseases and potential treatments and cures can first be tested on them. Other mammals have been engineered with the aim of potentially increasing their use to medicine and industry. These possibilities include pigs expressing human antigens aiming to increasing the success of

xenotransplantation Xenotransplantation (''xenos-'' from the Greek meaning "foreign" or strange), or heterologous transplant, is the transplantation of living cells, tissues or organs from one species to another.knockout mouse A knockout mouse, or knock-out mouse, is a genetically modified mouse (''Mus musculus'') in which researchers have inactivated, or " knocked out", an existing gene by replacing it or disrupting it with an artificial piece of DNA. They are importan ...

). This is possible since mice can be created with the same

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...

s that occur in human

genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders ...

s, the production of the human disease in these mice then allows treatments to be tested. The oncomouse is a type of

laboratory mouse The laboratory mouse or lab mouse is a small mammal of the order Rodentia which is bred and used for scientific research or feeders for certain pets. Laboratory animal sources for these mice are usually of the species ''Mus musculus''. They ...

that has been genetically modified developed by Philip Leder and Timothy A. Stewart of

Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...

to carry a specific

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

called an activated

oncogene An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels.

. Metabolic supermice are the creation of a team of American scientists led by Richard Hanson, professor of

biochemistry Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, a ...

Case Western Reserve University Case Western Reserve University (CWRU) is a Private university, private research university in Cleveland, Ohio, United States. It was established in 1967 by a merger between Western Reserve University and the Case Institute of Technology. Case ...

Cleveland, Ohio Cleveland is a city in the U.S. state of Ohio and the county seat of Cuyahoga County, Ohio, Cuyahoga County. Located along the southern shore of Lake Erie, it is situated across the Canada–United States border, Canada–U.S. maritime border ...

. The aim of the research was to gain a greater understanding of the PEPCK-C enzyme, which is present mainly in the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

and

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

s. In 4 March, 2025, Colossal biosciences announced they had successfully bred a " woolly mouse" as part of their ongoing efforts to produce the first genetically modified

elephant calf Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant ('' Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian elephant ('' Elephas maximus ...

with

mammoth A mammoth is any species of the extinct elephantid genus ''Mammuthus.'' They lived from the late Miocene epoch (from around 6.2 million years ago) into the Holocene until about 4,000 years ago, with mammoth species at various times inhabi ...

characteristics by the end of 2028.

Rats

A knockout rat is a rat with a single gene disruption used for academic and pharmaceutical research.

Goats

BioSteel is a

trademark A trademark (also written trade mark or trade-mark) is a form of intellectual property that consists of a word, phrase, symbol, design, or a combination that identifies a Good (economics and accounting), product or Service (economics), service f ...

name for a high-strength based fiber material made of the recombinant

spider silk Spider silk is a protein fibre or silk spun by spiders. Spiders use silk to make webs or other structures that function as adhesive traps to catch prey, to entangle and restrain prey before biting, to transmit tactile information, or as nest ...

-like protein extracted from the milk of

transgenic A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...

goat The goat or domestic goat (''Capra hircus'') is a species of Caprinae, goat-antelope that is mostly kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the ...

s, made by Nexia Biotechnologies. Prior to its bankruptcy, the company successfully generated distinct lines of goats that produced recombinant versions of either the MaSpI or MaSpII dragline silk proteins, respectively, in their milk.

Pigs

The enviropig is the trademark for a genetically modified line of Yorkshire pigs with the capability to digest plant phosphorus more efficiently than ordinary unmodified pigs that was developed at the

University of Guelph The University of Guelph (abbreviated U of G) is a comprehensive Public university, public research university in Guelph, Ontario, Canada. It was established in 1964 after the amalgamation of Ontario Agricultural College (1874), the MacDonald I ...

. Enviropigs produce the enzyme

phytase A phytase (''myo''-inositol hexakisphosphate phosphohydrolase) is any type of phosphatase enzyme that catalyzes the hydrolysis of phytic acid (myo-inositol hexakisphosphate) – an indigestible, organic form of phosphorus that is found in many pla ...

in the salivary glands that is secreted in the saliva. In 2006 the scientists from

National Taiwan University National Taiwan University (NTU; zh, t=國立臺灣大學, poj=Kok-li̍p Tâi-oân Tāi-ha̍k, p=, s=) is a National university, national Public university, public research university in Taipei, Taiwan. Founded in 1928 during Taiwan under J ...

's Department of Animal Science and Technology managed to breed three green-glowing pigs using

green fluorescent protein The green fluorescent protein (GFP) is a protein that exhibits green fluorescence when exposed to light in the blue to ultraviolet range. The label ''GFP'' traditionally refers to the protein first isolated from the jellyfish ''Aequorea victo ...

. Fluorescent pigs can be used to study human organ transplants,Staff (8 January 2008
Fluorescent Chinese pig passes on trait to offspring
AFP, Retrieved 31 August 2012 regenerating ocular

photoreceptor cell A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation ...

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

al cells in the brain,

regenerative medicine Regenerative medicine deals with the "process of replacing, engineering or regenerating human or animal cells, tissues or organs to restore or establish normal function". This field holds the promise of engineering damaged tissues and organs by st ...

via

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell ...

tissue engineering Tissue engineering is a biomedical engineering discipline that uses a combination of cells, engineering, materials methods, and suitable biochemical and physicochemical factors to restore, maintain, improve, or replace different types of biolo ...

, and other diseases. In 2015, researchers at the Beijing Genomics Institute used

transcription activator-like effector nuclease Transcription activator-like effector nucleases (TALEN) are restriction enzymes that can be engineered to cut specific sequences of DNA. They are made by fusing a TAL effector DNA-binding domain to a DNA cleavage domain (a nuclease which cuts DN ...

s to create a miniature version of the Bama breed of pigs, and offered them for sale to consumers. In 2017 scientists at the

Roslin Institute The Roslin Institute is an animal sciences research institute at Easter Bush, Midlothian, Scotland, part of the University of Edinburgh, and is funded by the Biotechnology and Biological Sciences Research Council. It is best known for creating ...

of the University of Edinburgh, in collaboration with

Genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

, reported they had bred pigs with a modified CD163 gene. These pigs were completely resistant to Porcine Reproductive and Respiratory Syndrome, a disease that causes major losses in the world-wide pig industry.

Cattle

In 1991,

Herman the Bull Genetically modified animals are animals that have been genetically modified for a variety of purposes including producing drugs, enhancing yields, increasing resistance to disease, etc. The vast majority of genetically modified animals are at t ...

was the first genetically modified or transgenic

bovine Bovines (subfamily Bovinae) comprise a diverse group of 10 genera of medium to large-sized ungulates, including Bos, cattle, bison, African buffalo, Bubalus, water buffalos, and the four-horned and spiral-horned antelopes. The members of this gro ...

in the world.Naturalis (2008). Herman the Bull stabled in Naturalis. Accessed on 3 January 2009 from www.naturalis.nl/naturalis.en/naturalis.en/i000968.html. The announcement of Herman's creation generated considerable controversy.Expatica News (2 April 2004). Herman the bull heads to greener pastures. Accessed on 3 January 2009 from http://www.expatica.com/nl/news/local_news/herman-the-bull-heads-to-greener-pastures--6273.html In 2016 Jayne Raper and her team announced the first trypanotolerant transgenic cow in the world. This team, spanning the International Livestock Research Institute,

Scotland's Rural College Scotland's Rural College (SRUC; ) is a Public university#United Kingdom, public land based college, land based Research university, research institution focused on agriculture and life sciences. Its history stretches back to 1899 with the estab ...

, the

's Centre for Tropical Livestock Genetics and Health, and the

City University of New York The City University of New York (CUNY, pronounced , ) is the Public university, public university system of Education in New York City, New York City. It is the largest urban university system in the United States, comprising 25 campuses: eleven ...

, announced that a Kenyan Boran bull had been born and had already successfully had two children. Tumaini – named for the Swahili word for "hope" – had been given a trypanolytic factor from a

baboon Baboons are primates comprising the biology, genus ''Papio'', one of the 23 genera of Old World monkeys, in the family Cercopithecidae. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow ba ...

via CRISPR/Cas9. p.276

Dogs

Ruppy (short for Ruby Puppy) was in 2009 the world's first genetically modified dog. A cloned

beagle The Beagle is a small breed of scent hound, similar in appearance to the much larger foxhound. The beagle was developed primarily for hunting rabbit or hare, known as beagling. Possessing a great sense of smell and superior tracking inst ...

, Ruppy and four other beagles produced a fluorescent protein that glowed red upon excitation with ultraviolet light. It was hoped to use this procedure to investigate the effect of the hormone

estrogen Estrogen (also spelled oestrogen in British English; see spelling differences) is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three ...

on fertility. A team in China reported in 2015 that they had genetically engineered

s to have twice the normal muscle mass, inserting a natural myostatin gene mutation taken from

whippet The Whippet is a British breed of dog of sighthound type. It closely resembles the Greyhound and the smaller Italian Greyhound, and is intermediate between them in size. In the nineteenth century it was sometimes called "the poor man's raceh ...

Primates

In 2009 scientists in

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

announced that they had successfully transferred a gene into a

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

species (

marmoset The marmosets (), also known as zaris or sagoin, are twenty-two New World monkey species of the genera '' Callithrix'', '' Cebuella'', '' Callibella'', and ''Mico''. All four genera are part of the biological family Callitrichidae. The term ...

s) and produced a stable line of breeding transgenic primates for the first time. It was hoped that this would aid research into human diseases that cannot be studied in mice, for example

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is an incurable neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. It typically presents as a triad of progressive psychiatric, cognitive, and ...

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...

and

schizophrenia Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...

Cats

In 2011 a Japanese-American Team created genetically modified green-fluorescent

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

s in order to study

HIV/AIDS The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...

and other diseases as

Feline immunodeficiency virus Feline immunodeficiency virus (FIV) is a lentivirus that affects cats worldwide and 2.5% to 4.4% of felines are infected. FIV was first isolated in 1986, by Niels C. Pedersen and Janet K. Yamamoto at the UC Davis School of Veterinary Med ...

(FIV) is related to HIV.Staff (3 April 2012
Biology of HIV
National Institute of Allergy and Infectious Diseases, Retrieved 31 August 2012

References

{{DEFAULTSORT:Genetically Modified Mammal Genetically modified organisms