Asexual Reproduction

In asexual reproduction there is no fusion of gametes and only one individual is needed as the parent. There is no mixing of genetic information and so no variation in the offspring. These genetically identical individuals are known as clones.
New plants can be produced quickly and cheaply by taking cuttings from older plants. These new plants are genetically identical to the parent plant.
Modern cloning techniques include:
-tissue culture using small groups of cells from part of a plant
-embryo transplants splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers
-fusion cell and adult cell cloning.


There are two types of reproduction, sexual and asexual. Only one parent is needed in asexual reproduction. Because of this the offspring are not a mixture of two individuals genes but have genes identical to their sole parent.

These individuals are called clones.

  

In the natural world it is nearly always better to get a mix of genes from two individuals. Many diseases are caused by faulty genes and healthy genes are usually dominant. The chance of avoiding these diseases is therefore better if your genes come from two individuals who are genetically very different.

Also, variation is a good thing. The offspring with the best qualities to cope with their environment will be the most likely to reproduce and so the species will prosper.

There are times when being able to clone oneself in nature is desirable, e.g. if a partner is not available. Strawberries clone themselves when they form new plants from runners. Worms and starfish can clone themselves.

Can we clone plants?
If a farmer has a fantastic tomato plant then he or she will want the offspring of that plant to be genetically identical to it so that they will have the same desirable characteristics. The simplest way to clone a plant is to take cuttings. Another method is called tissue culture.


from BBC Bitesize
Cut off part of the plant. Place the end in moist compost after dipping it in a growth hormone. Keep it warm and moist and you should have a new plant after a couple of weeks. From a small amount of the parent plant, perhaps just a few cells, many new plantlets can be grown if given the right conditions. Growth hormones are used to encourage the formation of new plants.

Can we clone animals?
A lot of advances have been made in this field very recently.

Embryo transplantation
 

We can take an embryo in its early stages, wait till it divides into 8 then split it into 4 separate 2 cell embryos. These are grown in the laboratory for a while then each one is inserted into a host mother. The offspring from these surrogate mothers will be genetically identical.

This was done to Tetra the monkey in 2000. Scientists hope to use this technique to study certain diseases. What better controlled variable can you have than genetically identical individuals?

Fusion Cell and Adult Cell Cloning

DNA is taken from one individual and put into an egg cell from another individual which has had its nucleus removed. This cell is then transplanted into a surrogate mother. The result is an individual which is identical to the one that donated the DNA. This is how Dolly the sheep was famously cloned in 1996.

                       

from BBC Bitesize

Fusion Cell - the DNA is taken from an embryo.

Adult Cell - the DNA is taken from some other cell, e.g. from the udder.