6.2.1: Cloning and biotechnology Flashcards
(43 cards)
What are clones?
Genetically identical whole organisms (e.g. identical twins, asexually produced bacterial offspring), single cells (e.g. inside the body that divide by mitosis) or genes (single genes inserted into plasmids/genomes of other organisms are copied and therefore referred to as clones).
Advantages of asexual reproduction
✔︎ Quick
✔︎ All offspring have necessary genes to survive in environment
✔︎ Don’t need to find a mate
Disadvantages of asexual reproduction
✖️No variation: only able to survive so long as the environment doesn’t change
Types of organisms that regularly use asexual reproduction
- Bacteria
- Fungi
- Plants (e.g. spider plants)
Clones are genetically identical to
the parent organism and each other
Example of simple cloning technique
Taking a plant cutting
How to make a plant cutting successful
- Use hormone rooting powder
- Make an oblique cut in the stem
- Keep cutting well watered
- Use a non-flowering stem
Examples of natural cloning in plants
- Bulbs in daffodils
- Runners (e.g. strawberry or spider plants): lateral stem grows away from parent plants, grows roots when touches ground, eventually becomes independent
- Rhizomes: e.g. marram grass; horizontal stem running underground grows buds that develop into vertical stems
- Stem tubers: e.g. potato; tip of underground stem swells to form tuber, buds on which produce new shoots
Why use natural cloning in horticulture?
- Faster than growing from seeds
* Can get genetically identical offspring from good stock
How are plants cloned commercially? (Give example for each)
- Cuttings (e.g. sugar cane)
- Grafting (e.g. roses)
- Micropropagation using tissue culture (e.g. orchids, bananas)
Micropropagation is an example of…
artificial cloning
When is micropropagation used?
- When the plants doesn’t readily produce seeds
- When the plant is rare
- When the plant doesn’t respond well to natural cloning
- When the plant is required to be ‘pathogen-free’ by growers (e.g. strawberries, bananas)
What is vegetative propagation?
production of structures in an organism that can grow into new individual organisms (doesn’t use sex organ structures)
Arguments for micropropagation
✔︎ Rapid production of large numbers of plants with genetic makeup for good yields
✔︎ Culturing meristem tissue produces disease-free plants
✔︎ Can produce new plants that are sterile and seedless to meet consumer tastes (e.g. grapes)
✔︎ Can reliably increase the number of rare or endangered plants
Arguments against micropropagation
✖️ Produces a monoculture (many plants are genetically identical and therefore susceptible to same genetic diseases/changes in conditions)
✖️ Expensive and requires skilled workers
✖️ Explants and plantlets are vulnerable to infection by moulds/other diseases during production process
✖️ If source material is infected with a virus, all clones will be infected
✖️ In some cases, large numbers of new plants are lost during the process
Micropropagation steps
1) Take small sample of tissue from the plant you want clones of.
⟶ Meristem tissue (usually virus-free) from shoot tips is often dissected in sterile conditions to avoid contamination by fungi and bacteria.
2) Material removed from plant = explant. Sample is sterilised (immersed in bleach/ethanol/sodium dichloroisocyanurate)
3) Explant is placed in sterile culture medium containing balance of plant hormones that stimulate mitosis. Cells proliferate, forming callus (mass of identical cells)
4) Callus is divided up. Cells from callus are placed in new culture medium, which has the mix of hormones and nutrients necessary to stimulate growth of tiny, genetically identical plantlets.
5) Plantlets are potted into compost and grow into small plants.
6) Young plants are planted out to grow and produce a crop.
Example of natural clones in animals
Twins formed by embryo splitting
Types of animal cloning
- Reproductive cloning (to generate new organisms)
* Therapeutic cloning (to generate cells/tissues/organs)
2 types of reproductive cloning
1) Artificial twinning
2) Somatic cell nuclear transfer (Dolly the sheep - developing technology)
Artificial twinning steps
1) Cow with desirable traits treated with hormones so she super-ovulates
2) IVF or artificial insemination (sperm from desirable bull), then embryos removed
3) Embryo develops to 16-cell stage (day 6); cells are still totipotent
4) Cells are separated and implanted into surrogate mothers
5) Offspring are clones of each other
Issue with artificial twinning
Result can still be unpredictable as sexual reproduction is involved (in the IVF or artificial insemination stage)
Reproductive cloning takes advantage of
the totipotent nature of embryonic stem cells
What is needed for somatic cell nuclear transfer?
- Tissue cell donor
- Unfertilised egg donor
- Surrogate mother
Somatic cell nuclear transfer steps
1) Nucleus is removed from somatic cell of adult animal
2) Nucleus is removed from mature ovum harvested from a different female of the same species (the cell is enucleated)
3) The nucleus from the somatic cell is inserted into the enucleated ovum and given a mild electric shock so it fuses and begins to divide
4) The embryo that develops is placed into the uterus of a surrogate mother animal
5) The new animal is a clone of the animal from which the somatic cell is derived, though its mitochondrial DNA will come from the egg cell
