UNIT 4: Animal Propagation and Animal Cloning

Exam Focus: Focus on the advantages of Artificial Insemination (AI) over natural breeding. The distinction between the two main cloning methods—**Somatic Cell Nuclear Transfer (SCNT)** and **Embryo Splitting**—is critical, as they produce genetically different results.

Table of Contents

1. Animal Propagation
   • Artificial Insemination (AI)
   • In-vitro Fertilization (IVF)
   • Embryo Transfer Techniques (ETT) (e.g. cow)
2. Animal Cloning
   • Definition of Animal Cloning
   • Somatic Cell Nuclear Transfer (SCNT)
   • Embryo Splitting

1. Animal Propagation

Methods used in animal husbandry and breeding programs to reproduce selected animals with desirable traits, often leveraging biotechnology to control the reproductive process.

Artificial Insemination (AI)

The process of mechanically depositing sperm into the female reproductive tract without natural copulation. The semen is collected from a superior male, processed, and often frozen for long-term storage.

In-vitro Fertilization (IVF)

Fertilization that occurs outside the body ("in glass"). Oocytes (eggs) are collected from the female and fertilized by sperm in a Petri dish under controlled laboratory conditions.

Embryo Transfer Techniques (ETT) (e.g. cow)

The process of collecting embryos from a genetically superior female (donor) and transferring them into the reproductive tract of recipient females (surrogate mothers) who carry them to term.

• **Procedure in Cattle:** The donor cow is superovulated (induced to produce multiple eggs). She is then artificially inseminated. The resulting embryos are non-surgically flushed from her uterus and transferred into synchronized recipients.
• **Goal:** To maximize the reproductive output of genetically superior females.

2. Animal Cloning

Definition of Animal Cloning

Animal cloning is the creation of a genetically identical copy of an animal or cells.

Somatic Cell Nuclear Transfer (SCNT)

This is the method used to create "Dolly the sheep" and is often referred to as **reproductive cloning**. It creates an organism genetically identical to the nucleus donor.

1. **Donor Cell:** A diploid nucleus is isolated from a **somatic cell** (e.g., mammary cell) of the animal to be cloned.
2. **Recipient Cell:** An unfertilized oocyte (egg cell) is obtained, and its original nucleus is removed (**enucleation**).
3. **Transfer:** The somatic nucleus is injected into the enucleated egg.
4. **Activation:** The reconstructed egg is stimulated (e.g., by electric pulse) to begin development as if it were a fertilized zygote.
5. **Implantation:** The developing embryo is transferred into a surrogate mother.

[Image of Somatic Cell Nuclear Transfer (SCNT) process]

Embryo Splitting (Blastomere Separation)

Also known as embryo twinning, this method creates multiple genetically identical animals from a single embryo.

• **Mechanism:** A multi-celled embryo (typically at the 4- to 8-cell stage) is physically divided into two or more identical halves. Each half is capped in a protective coat and implanted into a recipient female.
• **Result:** Produces **identical twins or triplets** (i.e., genetically identical to each other, but not identical to the nuclear donor parent).
• **Limitation:** The number of clones is limited by the number of blastomeres available.