Clones: exact copies used to describe genes, cells or whole organisms that have identical genetic material because they are derived from the same original DNA.
Examples- Identical twins NATURAL CLONES, produced when a zygote splits into two.
Plants reproduce ASEXUALLY forming runners.
ASEXUAL REPRODUCTION: mitosis in eukaryotes, binary fission in prokaryotes- the only genetic differences that can occur between asexually reproduced organsims result from mutations.
New organisms are formed with the same CLONED DNA.
Advantages of asexual reproduction.
- ITS QUICK: allowing organsims to reproduce rapidly and so take advantage of resources in the environment.
- It can be completed if sexual reproduction FAILS or is NOT POSSIBLE
- All the offspring have the genetic information to enable them to survive in their environment.
- DOESN'T PRODUCE ANY GENETIC VARIETY so any parental weakeness will be in all the offspring! If the environment changes ie. introduction of disease causing organism then all the genetically identical organisms will be EQUALLY SUSCEPTIBLE.
The production of structures in an organism that can grow into new individual organisms. Same genetic info as parent so are CLONES OF THE PARENT.
Example: English ELM are adapted to reproduce asexually following damage to the parent plant.
This means they can survive catastrophes such as disease or burning.
ROOT SUCKERS/BASAL SPROUTS grow from the meristem tissue in the trunk close to the ground where the least damage has occured.
- Root suckers help the elm to spread because they can grow all around the original trunk called a CLONAL PATCH which allows the patch to keep expanding as far as the resources allow.
- No genetic variation within the cloned population so natural selection CANNOT OCCUR making the new organisms just as vunerable to the disease that infected and killed the parent.
Artificial vegetative propagation.
Farmers and growers are able to artifically propagate valuable plants - 2 methods:
- Taking cuttings: section of stem cut between leaf joints: cut end of stem treated with plant hormones to encourage root growth and are planted. CLONE OF PLANT GROWS.
- Grafting: shoot section of woody plant is is joined to an already growing root= ROOTSTOCK the graft grows and it GENETICALLY IDENTICAL to parent plant but not the rootstock.
Artificial propagation using tissue culture.
Cuttings and grafts cannot produce huge numbers of cloned plants and it doesn't always work.
Using plant tissue culture can generate large numbers of genetically identical plants from a small amount of plant material.
Most common method is MICROPROPAGATION:
- UNDER STERILE CONDITIONS: Small piece of tissue, meristamatic cells, taken from the plant to be cloned, usually from the shoot tip. This is the EXPLANT.
- The explant is placed on a nutrient growth medium.
- Cells in the tissue divide but DO NOT DIFFERENTIATE- form a mass of undifferentiated cells called a CALLUS.
- After a few weeks callus cells removed and placed on a growth medium to encourage shoot growth.
- After a few more weeks growing shoots transferred onto a different growth medium to encourgae root growth.
- Growing plants transferred to a greenhouse to be acclimatised and grown further before they are planted outside.
Advantages and disadvantages of plant cloning.
- Farmers know what the crop plant produced will be like because it is cloned from plants with known features such as high yield, taste, colour and disease resistance .
- Farmers costs are redcued because the crop is ready to harvest at the same time
This is essentially a 'refinement' of selective breeding.
- The plants are genetically identical means they are equally susceptible to any pest, disease or environmental change.
EXAMPLE- Potato famine as fungus infected potato crop.
Cloning in animals.
In animals, only EMBRYONIC CELLS (Totipotent stem cells that are able to differentitae into any type of adult cell) are naturally capable of going through the stages in order to generate a new individual.
SPLITTING EMBROYS-artificial identical twins:
- Cells from a developing embryo can be separated out with each one produce a separate, genetically identical organism.
NUCLEAR TRANSFER- using enucleated eggs (eggs that have had their nucleus removed)
- The nucleus from a differentiated cell from an adult placed into an enucleated cell. Egg uses DNA from inserted nucleus to undergo dedvelopment.
EXAMPLE- Dolly the sheep. Cell taken from mamary gland of a ewe, nucleus transplanted into a cell from a second sheep and then inserted into a 3rd and then 4th sheeps uterus to develop.
Advantages and disadvantages of cloning animals.
- High value animals for example cows giving high milk yield can be cloned in large numbers.
- Rare animals can be cloned to perserve species.
- Genetically modified animals- eg sheep that produce pharmaceutical chemicals in their milk- can be quickly reproduced.
- Animal welfare not in mind- some strains of chickens cannot walk.
- As with plants- genetic uniformity makes the species unable to adapt to changes in environment.
- Still unclear whether animals cloned using the nuclear material from adult cells will remain healthy in the long term.
Non- reproductive cloning.
Cloned cells could be used to generate cells, tissues or organs to replace those damamged by disease or accidents.
- Being genetically identical to the individuals own cells means they will not be 'rejected' because the immune system will not recognise it as foreign.
- Could end the problems with waiting for donor organs to become avaliable for transplant.
- Cloned cells could be used to generate any type of cell because they are TOTIPOTENT.
- Less dangerous than a major operation such as heart transplant.
- Regeneration of heart muscle cells following a heart attack
- repair of nervous tissue destroyed by diseases such as multiple sclerosis
- repairing spinal cord of those paralysed by an accident that resulted in a broken back/neck
TECHNIQUES REFERRED TO AS THERAPUTIC CLONING.
Ethical objections to the use of human embryonic material.
Scientific concerns about a lack of understanding about how clones behave over time.