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School biology revision notes: CLONING - methods and uses

CLONING - tissue culture methods and uses explained

Descriptions of cloning techniques applied to plant tissue and animal tissue culture

 Doc Brown's school biology revision notes: GCSE biology, IGCSE  biology, O level biology,  ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old students of biology

 This page will help you answer questions such as ...  What are clones?   How do you make clones?   What are clones used for? What are the commercial advantages of cloning using animal or plant tissue culture?

Sub-index for this page

Methods of cloning plants

Making animal clones using embryo transplants

Cloning adult animal cells

Issues of concern about cloning animal cells - 'pros and cons'

See also more on genetic engineering - uses of  GM products

and a section on monoclonal antibodies

and a section on selective breeding of plants and animals



Methods of cloning plants

Note that selective breeding involves sexual reproduction, producing variable offspring - genetically varied.

This means the offspring might not inherit the desired characteristics you want.

Plant tissue culture produces genetically identical offspring (clones) of the parent plant - ensuring you know what their characteristics will be.

Plant stem cells from meristems can be used to make clones - so identical genetic copies of a plant can be grown quickly and cheaply.

See Hormone control of plant growth and uses of plant hormones  gcse biology revision notes

This means plant growers can grow crops of identical plants that have been genetically engineered to have more desirable features for farmers e.g. increased size of wheat grain, more disease resistant - but GM crops are also a controversial topic too!

Cloning has an important application in preserving rare species of plants - to grow more of those in danger of becoming extinct.

There are two ways of producing cloned plants.

 

tissue culture medium methods technique selected cells plantlets commercial growing1. Plant tissue culture technique

Tissue culture involves growing cells on, or in, an artificial growth medium like an agar jelly or liquid broth.

This enables you to grow whole plants from the cells of an individual plant - this can be done quickly, in relatively little space and all year round.

Method

You first select tissue cells from a plant which has the desirable characteristics you are interested in to clone - it can be a GM plant too.

They might be from a crop with good pesticide resistance, a tasty fruit/vegetable, an attractive flower.

The best tissue cells are obtained from fast-growing root or shoot tips - meristem tissues.

Here you put a few plant cells from the meristems into a dish of an artificial growth medium (agar gel) that contains nutrients and growth hormones including auxins. The agar supports the tiny plants.

The growth should be under aseptic (sterile) conditions to prevent growth of harmful microbes or fungus.

See Hormone control of plant growth and uses of plant hormones

The auxins promote growth by promoting cell division and cells grow quickly, elongating into new whole plants, all of which are clones of the original parent plant.

As the tissues grow shoots and roots they can be carefully be removed into potting compost and grown to full maturity.

These cloned plants can be grown very quickly using little space in a controlled nutrient medium and can be cultured at any time of the year - seasons don't count anymore!

Remember these are clones - genetically identical plants.

This tissue culture technique is used by or for:

(i) biology scientists (botanists in this case) to preserve rare plants in danger of extinction that are difficult to reproduce naturally - especially important now that many habitats are under threat from human activity in the landscape and unfavourable climate changes.

(ii) Horticulturalists can produce lots of stock of plants in their nurseries very efficiently and quickly.

(iii) You can use tissue culture to create genetically identical lines of plants with beneficial traits e.g. fruit taste, fruit yield, pesticide resistance - but these are NOT genetic modifications.

See also Hormone control of plant growth and uses of plant hormones  gcse biology revision notes

 

2. Using cuttings from plants

This is a traditional older method, and simpler to apply than the tissue culture described above.

Many experienced gardeners take cuttings (small sections of tissue) from good healthy parent plants and then plant the cuttings in compost containing hormones to produce genetically identical copies of the parent plants.

Method

The best tissue for this technique is obtained by slicing cuttings from fast-growing root or shoot tips (meristems tissues) or a cutting with a bud on it.

But it can be just a leaf and stem dipped in hormone powder to encourage rooting.

The cutting then grows into a new plant in composting material.

Hormone rooting powders are used to promote growth and they contain synthetic auxin hormones like NAA which promotes growth of new roots from the cutting.

See also Hormone control of plant growth and uses of plant hormones  gcse biology revision notes

The samples should be kept in moist conditions until ready for use.

Again, these plants can be produced quickly and cheaply both by professional or amateur gardeners.

 

3. Cloning using genetic engineering

genetic modification of plant cloning plant cells with desired trait gene inserted using a bacterium

e.g. sing the genetic modification of plant cells using a bacterium, then cloning the plant cells to produce a commercially viable plant.

Cloning of GM plant cells for desired characteristic is described on another GCSE biology notes page.

Important note on cloning:

After plant or animal cells have been genetically modified, it is essential that they transfer the newly introduced genes. Cells are first screened e.g. with an antibiotic, to kill cells that do not have the inserted gene. The cells can then be successfully cloned.

 

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Making animal clones using embryo transplants  (cross-check for overlap with other pages)

Farming uses many new methods thanks to advances in 'biotechnology' e.g.

Farmers can produce cloned offspring from their prize bulls and cows using embryonic transplants.

Sperm cells are removed from a prize bull and egg cells taken from a prize cow.

The sperm are used to artificially inseminate (artificially fertilise) the egg cells.

The embryo that develops can be split many times to form clones - but before any cells become specialised.

The cloned embryos can be then implanted into cows.

The embryos can then grow and develop in the normal natural way to produce lots of genetically identical baby calves.

'Theoretically', hundreds of ideal offspring can be derived every year from just one best bull and cow parents.


Animal tissue culture techniques - cloning adult animal cells

You can take an unfertilised egg cell and remove its nucleus in the technique of adult cell cloning.

The nucleus is extracted from an adult body cell (e.g. skin cell) and inserted into the 'empty' egg cell.

So you have replaced one nucleus with another, therefore changed the genome.

The egg cell is stimulated with an electric shock, causing it to divide, which is exactly what happens normal embryonic development.

When the embryo has developed into ball of cells, it is implanted into the womb of an adult female.

The embryo then grows into an identical copy of the original adult body cell and therefore a clone with the identical genetic information - same genome.

The most famous clone is Dolly the sheep, the forerunner of a scientific revolution!

Cloning animal cells using selected tissue

Important NOTE: Tissue culture cannot be used to grow a whole animal, BUT, it can be used to grow cells and tissues for medical research - one way of reducing controversial animal experiment testing e.g. of a new drug - under current UK law, new pharmaceutical products must be tested on whole animals, as well as tested on cultured animal tissues.

Method

A sample of the tissue is selected from an animal, made up of the cells you wish to study and use in your investigations e.g. a type of organ cell tissue's reaction to a new drug.

The cells you want are extracted from the tissue and separated from each other using enzymes.

The separated cells are added to a culture vessel of a growth medium containing all the nutrients that they need to grow and multiply.

After a number of cell divisions the sample can be split and further growth repeated in other vessels.

The cell tissue culture product can then be stored until required for experiments.

Animal tissue culture can be used in medical research to produce large quantities of cells in isolation from the rest of an animals body - no complications from the rest of the organism when conducting tests with them.

Using this animal cell culture technique, the product can be used to investigate the effects on it of chemicals, e.g.

a particular substance such as a toxin or drug,

a change in the environment e.g. pH,

and so monitor the effects of these factors on specific tissue cells without the complications of other types of cells and processes going on in a whole organism.

You can use these cells to conduct experiments e.g. the effect of drugs or any other chemical substances on the specific cells.

e.g. the effect of glucose on pancreatic cells grown in the culture medium.

You can look at the health of cells in different mediums - effectively different environments.

You can infect the cells with a virus to help develop vaccines - the invasive virus multiplies in cells, ultimately destroying them - this initially avoids testing a new vaccine on human beings until later, if results from tissue culture cells prove active against a virus.


Issues of concern about cloning animal cells - 'pros and cons'

(a) Although cloning enables you to produce plenty of supposedly 'ideal' offspring, there is a genetic price to pay.

Using cloning techniques, you do reduce the 'gene pool'.

This means there are fewer alleles in the population and consequently the animal is more susceptible to various disorders.

When members of a population are so closely genetically related, and encounter a new disease, the whole population can be affected, possibly fatally.

The animal's genome may not have the alleles necessary to offer some resistance - protection against the disease.

Cloned animals might not be as healthy as normally produced offspring.

e.g. Dolly the sheep had arthritis which you expect in old age in many animals.

There are other cases where animal's organs do not seem to function as well as expected.

These effects are not that well understood at the moment.

(b) One important use of cloning is to help preserve endangered species of animals.

Cloning could be used to reproduce endangered animal species, whose numbers were falling dangerously low i.e. in danger of extinction.

(c) Research on cloning animals has led to a greater understanding of embryo development and also the process of ageing and age-related disorders.

(d) There is concern that attempting to clone humans might not be very successful.

Because of the reduced gene pool, the offspring may be more likely to suffer from genetic disorders including babies born with severe disabilities.

(e) Cloning mammals is proving a means of providing organs for transplants.

e.g. genetically modified pigs can be bred to provide donor organs for humans and cloning the pigs could meet the ever increasing demand from critically ill patients on the waiting list.

 

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Typical learning objectives for this page

  • Know and understand that asexual reproduction can be used to produce individuals that are genetically identical to their parent.

  • Appreciate that scientists can now add, remove or change genes to produce the plants and animals they want.

    • You are expected to use your skills, knowledge and understanding to:

      • interpret information about cloning techniques and genetic engineering techniques,

        • In the exam you may be given data to work from,

      • make informed judgements about the economic, social and ethical issues concerning cloning and genetic engineering, including genetically modified (GM) crops.

  • Know and understand that new plants can be produced quickly and cheaply by taking cuttings from older healthy plants.

    • These new plants are genetically identical to the parent plant, ie clones or identical copies.

      • The cuttings are taken with a new bud on and planted in good quality moist compost where your cloned plant cutting should grow into a healthy new one.

  • Know and understand that modern cloning techniques include:

    • Tissue culture using small groups of cells from part of a plant.

      • Cells from part of a plant are grown in a suitable nutrient medium with added growth hormones.

      • These can be grown quickly, cheaply in large quantities at any time of the year.

    • Embryo transplants splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers.

      • Agriculture is using artificial insemination to produce high quality cattle - cloned offspring of prize bull - a lot of money can change hands over a prize bull eg hiring a prize bull for its sperm!

      • Egg cells from a 'prize cow' are artificially fertilised by sperm cells from the 'prize bull'.

      • After the resulting embryo has developed is split to form embryonic clones which can be implanted in other cows, who have become, 'artificially', the host mothers.

      • This means multiple quality offspring can be produced efficiently without waiting too long for 'mother nature'!

        • Cloning is a type of asexual reproduction producing cells that are genetically the same as the original starting cell.

        • Cloning reuses the same gene pool and so the gene pool is narrowed and if an organism (eg cattle) become susceptible to a disease, there are no animals in the herd to resist it.

        • Cloning can be used to help preserve endangered species.

    • Adult cell cloning the nucleus containing the genetic material is removed from an unfertilised egg cell.

      • Know that this nucleus from an adult body cell, eg from a skin cell, is then inserted into the egg cell from which the original nucleus was removed ie the egg cell nucleus has been replaced with a complete set of chromosomes.

      • An electric shock stimulus then causes the egg cell to begin to divide to form embryo cells, just as a normal embryo would do.

      • These embryo cells contain the same genetic information as the adult skin cell.

      • When the embryo has developed into a ball of cells, it is inserted (implanted) into the womb of an adult female (surrogate mother) to hopefully continue its development from embryo ==> foetus ==> baby.

      • Although cloning is a successful technique, it is not without problems and raises social and ethical issues.

      • Cloning involves retaining the same restricted pool of DNA but it is providing valuable research into embryo development and cell aging and age related disorders.

      • Cloning mammals inevitably produces a reduced gene pool whereas sexual reproduction provides genetic variety.

      • The limited pool of alleles which make up chromosomes can make the species more susceptible to a contracted disease and other conditions such as premature aging, organ and immune system failures etc. (Look up the case of 'Dolly the Sheep').

      • The rate of successful cloning very low, genetic defects are common and those animals which survive the cloning procedure are often unhealthy and are much more susceptible to disease i.e. they are a 'genetically weak' animal.

      • If human cloning was attempted, it could lead to babies being born with disabilities, there is only a certain chance that an embryo would develop into a completely normal healthy baby - an ethical and moral dilemma for potential parents and the medical profession.

      • Cloning mammals is a means providing organs for transplants e.g. genetically modified pigs could be bred to provide donor organs for humans and cloning the pigs could meet the ever increasing demand from critically ill patients on the waiting list.

      • Cloning could be used to reproduce endangered animal species, whose numbers were falling dangerously low i.e. in danger of extinction.

  • Revise any practical work you did to develop skills and understanding which may have included (which should also be revised, helps in understanding 'how science works' and context examination questions):

    • investigating the optimum conditions for the growth of cuttings, of, eg Mexican hat plants, spider plants, African violets,

    • investigating the best technique for growing new plants from tissue cultures (eg cauliflower).

 

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