Principles involved in cloning

Method

• Eggs taken (from pedigree cow) and fertillised (using sperm from a pedigree bull) in a petri dish
• They divide to form a ball of cells
• The ball of cells (young embryo) are split into individual cells.
• Each cell develops into an embryo genetically identical to the original.
• They are implanted into surrogate mothers.

Benefits

Enables farmers to increase their stock.
Can conserve rare breeds.

Disadvantages

You cannot guarantee the genotype of the offspring. 

Method

• Cells taken from the tissue of a donor and put in a medium which stops division.
• Unfertilised egg taken from the recipient and nucleus removed.
• Enucleated egg and somatic cell fused together using an electric charge.
• Divides to form a ball of cells.
• Implanted into a surrogate mother.
• Individual born is genetically identical to the donor.

Benefits

Enables desirable qualities to be conserved for future generations.
Allows many genetic copies to be produced- genetic stock
Cross-breeding isn't full-proof, this is the only way to guarantee the genotype.

Disadvantages

Expensive and unreliable
Long-term unforeseen effects such as premature ageing? 

The technique of growing cells in a laboratory using an appropriate growth medium.

Cells which divide as adults:

• skin cells to repair wounds
• blood cells
• digestive cells which are worn away

Tissue engineering: growing living cells on a framework of synthetic material to produce a tissue e.g. skin tissue for deep burns.
(Other applications= blood vessel replacement, treatment of nerve diseases)

Stem cells: Undifferentiated cells capable of giving rise to different types of specialised cells. Found in adult bone marrow but the best ones are found in embryos.

 Therapeutic stem cell cloning could have huge medical benefits.  

Method

• Mature cell taken from patient.
• Nucleus removed
• Nucleus removed from human ovum.
• Mature cell nucleus transferred to the ovum
• Ovum (containing patient's DNA) divides to form a ball of stem cells.
• Stem cells isolated and cultured.
• Stem cells grow into the required organ or tissue.

Benefits

Contains patient's DNA so no risk of rejection
Organ donor shortages.

Disadvantages

Ethical issues with using embryos.

Relies on the fact that plant cells are TOTIPOTENT (can differentiate as adult cells)

Method

• Meristem of plant removed with scalpel.
• Meristem cut into explants (small pieces)
• Explants put on sterile, aerated growth medium.
• Cells divide by mitosis to form a callus
• Callus subdivided and each piece allowed to develop into a plantlet.
• Plantlet transplanted to sterile soil when they are a suitable size.

Benefits

Large numbers are grown in sterile conditions- ensuring high survival rate.
Good quality stock with favourable qualities (e.g. disease resistant, high yield)
Uniform crop
Large numbers stored in a small area-reduced heating/lighting cost
Unique genotypes preserved
Less space needed for transport
Healthy plants are selected so plant diseases can be eliminated

Disadvantages

Regular inspections needed to remove defective plants - high labour cost
Sterile conditions must be maintained (any infection damages lots of plants)
Genetically unstable so mutations may occur.