BY5.6 Cloning

Cloning

A clone is a group of genetically identical organisms formed from a single parent as a result of asexual reproduction or by artificial means. Cloning in nature is common, e.g. division of bacteria.

Cloning of Animals

Animals are cloned using a number of different methods.

Embryo Cloning

Consider a cow being used for its high milk yield. Eggs are collected from the cow, and fertilised in vitro (in a petri dish) using sperm collected from bulls from parentage with high milk production. A blastocyst forms which is broken up into individual embryos.  These are implanted into surrogates. Many identical offspring are produced-the offspring are clones of one another.

Nuclear Transfer

Using nuclear transfer, genetic copies of an individual can be made.

In this method, somatic cells are taken from the donor (the organism to be cloned) and cultured in a solution which stops cell division (so that the cells have the right number of chromosomes etc). An unfertilised ovum from the recipient is enucleated, so there is a nucleus-free egg cell. The cells are mixed and a gentle electric pulse is applied, causing them to fuse. The resulting zygote is allowed to form a blastocyst/embryo. The embryo is genetically identical to the donor. This embryo is implanted into a surrogate, possibly the recipient, and is born after the gestation period.

Advantages and Disadvantages

• Cell culture can produce many identical cells, e.g. cancer cells, for research.
• A long indentical genetic line means that favourable characteristics remain in genetic stocks.

• In mammals this technique doesn't always work and is very expensive.
• The donor may have genetic disadvantages, eg recessive alleles for diseases
• Offspring produced by this method may suffer premature aging or other negatove side effects.

Tissue Culture

Tissue culture is used to make cells, such as cancer and stem cells, to divide in vitro, in the lab. They are genetically identical to the organism from which they are taken.

Once differentiated, many cells such as nerve cells won't divide. That's why stem cells are used for this type of culture, because they are undifferentiated.

During tissue culture, growth conditions are carefully and meticulously controlled. Ionic balance and water potential must be controlled. These conditions can be used to cause cells to differentiate--this is tissue engineering, for example: tissues grown on a special synthetic framework under the right conditions can be used to make a layer of skin, used for an appligraf. Tissue engineering can also be used to repair blood vessels and cartilage as well as treat degenerative nerve diseases. These tissues won't be rejected when applied as they are genetically identical to the donor. It is hoped that…