Welcome to the Chapter on Cloning!

Hello future Biologists! This chapter, Cloning, is an exciting part of studying how we use biological resources effectively. Don't worry if the word "cloning" sounds like science fiction; in reality, it is a powerful set of techniques we use in agriculture and medicine to create identical copies of organisms.

In this lesson, we will explore both natural and artificial methods of cloning plants and animals, including micropropagation and somatic cell nuclear transfer.

Let's dive in and learn how to make biological copies!

What Exactly is a Clone?

In simple terms, a clone is an organism or cell that is genetically identical to another organism or cell. This means they have the exact same DNA code.

Key Takeaway: Cloning is essentially a form of asexual reproduction, where offspring are produced from a single parent and have identical genetic information.

Section 1: Natural Cloning in Biology (A Review)

Cloning isn't just something done in a lab; nature does it all the time! When organisms reproduce asexually, they are naturally cloning themselves.

Natural Cloning in Plants

Many plants make identical copies of themselves without seeds or pollination:

  • Runners: Think of strawberry plants. They send out horizontal stems called runners, and where the runner touches the ground, a new, genetically identical plant develops.
  • Bulbs and Tubers: Onions (bulbs) or potatoes (tubers) are storage organs that can grow into new, identical plants the next season.


Why is this useful? If a plant is well-adapted to its environment, natural cloning allows it to quickly colonise an area and pass on those successful traits.

Section 2: Artificial Cloning of Plants (Micropropagation)

When humans clone plants, we often want to mass-produce commercial quantities of a plant with specific, desirable traits (such as high yield, disease resistance, or pest resistance).

Method 1: Cuttings (The Simplest Approach)

This is the traditional method used by gardeners:

  1. A short section of the stem (a cutting) is removed from the parent plant.
  2. The cutting is often dipped into rooting powder (containing plant hormones like auxins).
  3. It is placed in moist soil or compost to grow into a new plant.

Method 2: Micropropagation (Tissue Culture)

Micropropagation is a commercial method used to produce thousands of identical plants from small pieces of plant tissue grown in vitro (in glass or sterile laboratory containers) under sterile conditions.

Analogy: If taking a cutting is like making one copy on a slow photocopier, micropropagation is like running an industrial printing press!

Step-by-Step: How Micropropagation Works
  1. Selection and Explants: Small pieces of plant tissue, called explants (usually taken from the tips of stems or side shoots), are cut from the parent plant.
  2. Sterilisation: The explants are surface-sterilised using a disinfectant to kill any bacteria or fungi (aseptic technique).
  3. Nutrient Agar (In Vitro): The explants are placed in sterile agar medium containing nutrients (such as glucose, amino acids, and inorganic ions) and plant growth hormones (auxins and cytokinins).
  4. Callus Formation and Shoot Growth: The cells divide by mitosis to form a mass of undifferentiated cells (a callus), which then develops into shoots.
  5. Rooting: The shoots are transferred to a medium with a different balance of hormones to stimulate root growth, producing small plantlets.
  6. Acclimatisation: The plantlets are transferred to compost in glasshouses or polythene tunnels, where they are protected as they grow into mature, identical commercial crops.
Quick Review: Plant Cloning (Micropropagation)

Micropropagation allows commercial growers to produce large numbers of genetically identical, disease-free plants rapidly at any time of the year.

Section 3: Artificial Cloning of Mammals

Cloning mammals involves introducing a diploid nucleus from a body cell into an enucleated egg cell. The most famous example is Dolly the sheep, the first mammal successfully cloned from an adult body cell.

Step-by-Step: Production of Cloned Mammals
  1. Obtaining the Diploid Nucleus: A mature somatic (body) cell is taken from the animal to be cloned (Animal A). The diploid nucleus containing the complete genetic information is extracted.
  2. Preparing the Egg Cell (Enucleation): An unfertilised egg cell is taken from another female (Animal B). Its haploid nucleus is removed, leaving an enucleated egg cell.
  3. Transfer and Electric Shock: The diploid nucleus from Animal A is inserted into the enucleated egg cell. An electric shock or pulse is applied to fuse them and stimulate the egg cell to start dividing by mitosis.
  4. Embryo Development: The dividing cell develops in vitro into an early-stage embryo (a ball of cells).
  5. Implantation into a Surrogate Mother: The embryo is implanted into the uterus (womb) of a surrogate mother (Animal C).
  6. Birth of the Clone: The surrogate mother gives birth to an offspring that is genetically identical to Animal A (the donor of the diploid nucleus).
Key Exam Summary:
• Diploid nucleus donor: provides all the genetic material (clone is identical to this animal).
• Egg donor: provides the enucleated egg cell cytoplasm and organelles.
• Surrogate mother: carries the embryo to term.

Section 4: Uses, Advantages, and Disadvantages of Cloning

Cloning has vital applications in agriculture, medicine, and biotechnology, but also presents significant limitations.

Uses and Advantages of Cloning

  • Commercial Micropropagation of Plants:
    • Rapid mass-production of plants with desirable characteristics (e.g. pest resistance, high crop yield).
    • Production of disease-free plant stocks all year round.
  • Cloning Transgenic Animals to Produce Human Proteins:
    • Transgenic animals (animals that have had genes from another species, such as humans, transferred into their DNA) can be engineered to produce valuable human proteins (such as human antibodies, insulin, or blood clotting factor VIII) in their milk or blood.
    • Cloning these transgenic animals ensures that the valuable human gene is retained and passed on to an entire herd without being lost through sexual reproduction, allowing commercial extraction of life-saving medical proteins.
  • Preserving Superior Livestock: Preserving elite breeding lines in farm animals that have high milk yield or lean meat production.

Disadvantages and Ethical Issues

  • Lack of Genetic Variation: Cloned populations share identical DNA. If a new pathogen or environmental change emerges, all individuals are equally susceptible, which can wipe out the entire crop or herd.
  • Low Success Rate in Mammals: Cloning mammals is technically difficult, expensive, and has a very low success rate, with many embryos failing to develop.
  • Animal Welfare Concerns: Cloned mammals may suffer from developmental abnormalities, health complications, and reduced lifespans.
  • Ethical Issues: Human cloning is widely banned due to moral, ethical, and safety concerns.
Key Takeaway Summary

Micropropagation produces large numbers of identical plants in vitro from explants. Mammal cloning transfers a diploid nucleus into an enucleated egg cell, stimulated by an electric shock and grown in a surrogate mother. A key application is cloning transgenic animals to produce useful human proteins.