Reproduction

• Sexual Reproduction- Resemble their parents (not identical) 
• ASexual Reproduction- Clones which are genetically identical to their parents

Organisms have sex cells called gametes. Humans- Sperm and eggs.

Fusion

• Sexual reproduction happens when a male and female gamete join. ( Fertilisation) 
• Allows some of the genetic information from each parent to mix
• Producing offspring that resemble their parents but are not identical to them.
• Sexual reproduction leads to variety in offspring

In human beings, each gamete contains 23 chrosomes, half the number found in the other cells in the body. 

When the female and male gametes fuse, the new embryo contains the full 26 chromosomes- half from the father and half from the mother

Asexual Reproduction only needs one parent. Since there is only one parent there is no fusion of gametes and no mixing of genetic information. So the offspring are genetically identical to the parent and to each other. They are clones. 

Plants

Asexual reproduction in plants  can take place in many different ways. 

Many plants develope underground food storage organs that later develop into the following years plants. 

Some plants produce side branches with plantlets on them. (Busy Lizzy does this)

Other plants, such as strawberries produce runners, which plantlets on them.

Animal

Asexual reproduction in animals is less common than sexual reproduction but does happen in sea anemones and starfish.

Cuttings

• Simplest way to clone a plant. 
• Branch from the parent plant is cut off, its lower leaves removed and the stem planted in damp compost. Plant hormones are often used to encourage new roots to devleop. 
• The cutting is usally covered in a clear plastic bac at this stage to keep it moist and warm. 
• After a few weeks, new roots develop and a new plant is produced.

Tissue Culture 

• Uses tiny peices of the parent plant. 
• Sterile agar elly with plan hormones and lots of nutrients are needed 
• This makes tissue culture more expensive and difficult to do than cuttings 

Embryo Transplants

• Developing embyro is removed from a pregnant animal at an early stage, before the embryos cells have had time to become specialised.
• The cells are seperated from one another.
• They are then grown for a while in a lab and transplanted back into host mothers
• When offspring are born they are identical to eachother and genetically related to the original pregnant animal. 

Adult cell cloning 

• Nucleus is removed from an unfertilised egg and discarded
• The nucleaus is removed from an adult body cell and injected into the egg cell
• An electric shock is applied to make the egg cell begin to divide to form an embyro 
• While it is still a ball of cells, the emybro is inserted into the womb of an adult female
• The embyro continues to grow and develop

The new individual is genetically identical to the animal that donated the nucleaus from one of its body cells 

• Produces a unique set of genes 
• Genes can be swapped across species 

How it works

• Certain enzymes cn cut peices of DNA from one organism, and join them into a gap in the DNA of another organism 
• This means the new organism with the inserted genes has the genetic information for one or more new characteristics. 
• e.g. The organism might produce a useful substance, or carry out a newn function.

Genetic Modification works in animals, plants and microorganisms. e.g. New genes can be transferred to crop glants to make GM crops. Some GM crops are resistant to certain weed killers, while others are reisistant to insect pests.

Strong arguments for and against genetic modification of crop plants. GM crops generaly have increased yields, useful for feeding a growing population.