Transgenic Animals
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Direct answer
A transgenic animal is one whose genome has been deliberately manipulated to carry and express a foreign gene. Over 95 per cent of existing transgenic animals are mice, the field's workhorse. NCERT lists their major uses: studying normal physiology and development (how a gene's product shapes body function), building models of human diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's, producing useful biological products, testing vaccine safety before human use, and testing chemical safety, since transgenics are more sensitive to toxic substances than ordinary animals. The flagship example is Rosie, the first transgenic cow (1997), whose milk contained human alpha-lactalbumin at about 2.4 grams per litre — a nutritionally superior product for human babies.
What you must remember
- Definition: animals with DNA manipulated to possess and express an extra (foreign) gene — the genome plus a payload it did not evolve.
- The 95 per cent figure: mice constitute the overwhelming majority of transgenic animals — a one-liner lifted straight from NCERT.
- Physiology and development studies: inserting or deleting genes reveals their roles in normal body function and development.
- Disease models: transgenic lines mimic human diseases — cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's disease are NCERT's named four — permitting testing of therapies in animals.
- Biological products: Rosie, the first transgenic cow, produced human alpha-lactalbumin-enriched milk (about 2.4 g per litre), nutritionally more balanced for human babies than ordinary cow milk.
- Vaccine safety: transgenic animals are used to check vaccine safety before release for human use.
- Chemical safety: transgenics show greater sensitivity to toxic substances, so they detect pollution-level toxicity that standard test animals would miss.
- Distinguish from clones: Dolly was a clone (identical nuclear copy), not transgenic; a transgenic animal carries foreign DNA — exam decoys conflate the two.
How Rosie's milk was made better
Rosie's story is the cleanest narrative in the chapter. Human breast milk owes part of its infant-suitability to alpha-lactalbumin, a protein abundant in human milk but not in cow milk. Scientists inserted the human gene encoding this protein into a dairy cow's genome under control of a mammary-gland-specific promoter, so the foreign gene would switch on where milk is made. Rosie, born in 1997, secreted milk containing roughly 2.4 grams of human alpha-lactalbumin per litre — a product closer in composition to human milk and, as NCERT puts it, nutritionally more balanced for human babies. The deeper message is the strategy: the mammary gland as a bioreactor, a living factory that harvests a valuable human protein in a food the world already collects daily.
The rest of the uses extend the same logic of purpose-built animals. A mouse engineered to overexpress or lack a single gene becomes a living experiment on that gene — normal physiology and development read directly in fur, bone and behaviour. When the manipulated gene is a human disease gene, the mouse contracts a version of the illness — NCERT names cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's. Safety testing exploits heightened sensitivity: a transgenic animal carrying a reporter or susceptibility gene responds to toxins at lower doses, so chemicals and vaccines can be screened for danger before humans ever receive them. One technology, five applications — and the exam's list question expects all five, in NCERT's words.
Where the marks leak
The list itself is the paper: "which of the following is not a use of transgenic animals" routinely offers food production or xenotransplantation as the odd one out against NCERT's five uses. The Rosie facts leak in halves — students remember "Rosie, transgenic cow" but not the protein (human alpha-lactalbumin) or the number (2.4 g/L); both halves appear in options. The 95 per cent mice figure is tested as a statement ("most transgenic animals are mice" — true). The Dolly decoy deserves respect: Dolly the sheep was produced by somatic cell nuclear transfer, a cloning milestone carrying no famous foreign gene — a question asking "which of these is a transgenic animal" among Dolly, Rosie and a normal F1 hybrid expects Rosie. Finally, keep the disease-model names exact, because cousins like muscular dystrophy sit in the options as bait.
Frequently asked questions
Which animal accounts for most transgenic animals worldwide?
Mice — more than 95 per cent of all transgenic animals, owing to small size, short generation time and well-mapped genetics.
What was special about Rosie the transgenic cow?
She produced human protein-enriched milk containing about 2.4 g per litre of human alpha-lactalbumin, more nutritionally suitable for human babies.
List the major uses of transgenic animals per NCERT.
Studying normal physiology and development, modelling human diseases, producing biological products, testing vaccine safety and testing chemical safety.
Name the human diseases for which NCERT cites transgenic models.
Cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's disease.
How is a transgenic animal different from a clone?
A transgenic animal carries and expresses foreign DNA; a clone like Dolly is a genetic copy of a single parent produced without adding any foreign gene.