CloningIB MYP Biology: Revision notes

A clone is an organism that is genetically identical to its parent. Clones are produced by asexual reproduction: there is only one parent, no gametes fuse and no genes are mixed, so the new cells are made by mitosis and each one receives an exact copy of the parent's DNA.

Identical twins are natural clones. Cloning in biotechnology means making clones on purpose, in plants or in animals.

A cutting is a piece of stem or shoot cut from a parent plant. It is often dipped in rooting hormone and planted in moist compost. The cut stem grows roots and becomes a new plant that is a clone of the parent.

• Cheap and simple, so it is used by gardeners and farmers
• Quickly gives many plants with the same useful characteristics, such as high yield or flower colour
• Only a few cuttings can be made from one plant

In tissue culture, a tiny piece of tissue is cut from a parent plant and placed on sterile jelly containing nutrients and plant hormones. The cells divide by mitosis and grow into a new plantlet, which can be planted out when it is big enough.

The method must be sterile so that bacteria and fungi do not grow on the nutrient jelly and kill the plantlets.

• Thousands of identical plants can be made from a very small amount of tissue
• Plants can be grown all year round
• Useful for rare or endangered plants and for plants that are hard to grow from cuttings
• Disease-free plants can be produced

In embryo transplant, a fertilised egg from two high-quality parents is allowed to divide into a ball of a few cells. The cells are split into separate embryos, and each embryo is placed in the uterus of a surrogate mother, who gives birth to the young. The young are clones of each other, but not clones of either parent, because the embryo came from the fusion of gametes.

This is used to produce many offspring from the best breeding animals, for example cattle.

Adult cell nuclear transfer makes a clone of an adult animal. This is how Dolly the sheep was produced in 1996.

1. Take an unfertilised egg cell from one animal and remove its nucleus.
2. Take a body cell (such as an udder cell) from the animal to be cloned and take out its nucleus.
3. Put the donor nucleus into the empty egg cell.
4. Give the cell a small electric pulse to make it start to divide into an embryo.
5. Implant the embryo into the uterus of a surrogate mother.

The offspring has the genes of the animal that gave the body cell nucleus, so it is a clone of that animal.

Uses: copying animals with high milk or meat yield; producing animals that make medicines in their milk; saving endangered species; copying rare, high-value plants quickly.

Issues:

• Clones have no genetic variation, so one disease could wipe out all of them.
• Cloning animals has a low success rate and is expensive.
• Some cloned animals have health problems or a shorter life, which is an animal welfare concern.
• Some people think it is wrong to interfere with natural reproduction, and worry that humans might be cloned.

When you discuss cloning, give benefits and drawbacks and then reach a conclusion.