Production of transgenic animals.

What are Transgenic Animals?

A transgenic animal is one that carries a recombinant gene (DNA) introduced into its genome. This recombinant DNA, or transgene, can come from a different species, allowing for the transfer of desired traits. The transgene is integrated into the animal’s DNA and passed on to subsequent generations.

Methods of Production

Several techniques are used to create transgenic animals. Here's a breakdown:

1. Microinjection

This was the initial method used. It involves directly injecting DNA into the pronucleus of a fertilized egg. The egg is then implanted into a surrogate mother. This technique is commonly used in mice and pigs.

• Process: DNA is mixed with a carrier solution and injected directly into the pronucleus (the male and female nuclei) of a fertilized egg.
• Efficiency: Relatively low success rate (around 1-5%).

2. Viral Vectors

Modified viruses (e.g., retroviruses, adenoviruses) are used to deliver the transgene into the animal’s cells. The virus’s disease-causing genes are removed, leaving only the genetic material to carry the transgene.

• Process: Viral vectors infect cells, delivering the transgene into the host's genome.
• Advantages: Can target specific tissues more effectively than microinjection.

3. Somatic Cell Nuclear Transfer (SCNT) - Cloning & Transgenesis

This technique, famously used to clone Dolly the sheep, can also be used to create transgenic animals. The nucleus of a somatic cell (e.g., skin cell) is transferred into an enucleated egg cell (an egg cell with its nucleus removed). The resulting embryo is then implanted into a surrogate mother. The somatic cell's DNA incorporates the transgene.

• Process: A somatic cell (e.g., fibroblast) containing the transgene is taken. Its nucleus is transferred to an enucleated egg cell. This zygote is then implanted into a surrogate mother.
• Significance: Allows for the creation of transgenic animals with desired traits from adult cells.

4. CRISPR-Cas9 Gene Editing

While not strictly transgenic animal *production*, CRISPR-Cas9 can be used to precisely edit existing genes within an animal's genome, creating targeted genetic modifications. This is increasingly important in creating animals with specific traits or disease models.

Applications of Transgenic Animals

Transgenic animals have diverse applications:

• Pharmaceutical Production (Biopharming): Transgenic animals can produce therapeutic proteins in their milk, blood, or other tissues (e.g., goats producing human antithrombin).
• Agricultural Improvement: Transgenic livestock can be created with enhanced growth rates, disease resistance, or milk production.
• Disease Models: Transgenic animals can be engineered to mimic human diseases, facilitating research and drug development.
• Xenotransplantation: Genetically modified pigs are being explored as potential sources of organs for human transplantation.

Ethical Considerations

The creation of transgenic animals raises ethical concerns:

• Animal Welfare: Concerns about the potential for suffering and unintended consequences.
• Genetic Diversity: Potential impact on the genetic diversity of animal populations.
• Food Safety: Concerns about the safety of consuming products from transgenic animals.

Method	Description	Advantages	Disadvantages
Microinjection	Direct injection of DNA into pronucleus	Simple, early technique	Low efficiency, random integration
Viral Vectors	Using modified viruses to deliver DNA	Targeted delivery	Potential for viral infection
SCNT	Nuclear transfer from somatic cell	Allows for creation from adult cells	Technically challenging