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6.4 Cloning and Biotechnology
6.4.1 Natural Clones in Plants
- Vegeta&ve reproduc&on = plants produce asexually using meristem cells
- Vegeta&ve organs of plants include root and shoot &ps, axillary buds (where stem and leaves meet),
vascular cambium (between xylem and phloem)
- Over &me a young miniature plant forms at the vegeta&ve organs -> remains aAached as a clone of the
parent plant (no other DNA introduced) -> when mature it detaches and can live independently
- New plants all have the same phenotype = easier growing/harves&ng especially if hard to grow from seeds
- Some plants have horizontal stems/runners so new plants are not overshadowed by the parent/in
compe&&on for water and nutrients
- Adven&&ous roots form under nodes of runners which die when the plantlet is self-sustaining
Propaga:on techniques using vegeta:ve reproduc:on
- Asexual reproduc&on doesn’t require seeds as it is not sexual reproduc&on – can use tubers, rhizomes,
bulbs, suckers, offsets -> all contain modified stems that can generate meristema&c &ssue
1. Tubers: potato tubers are swollen modified roots that form eyes on their surface that can sprout new
growth (chiRng) from starch stored in tubers
2. Rhizomes: ginger forms rhizomes – modified horizontal underground stems – that form new stems
and adven&&ous roots
3. Bulbs: used by onion and garlic to grow adven&&ous roots underground and shoots above ground
4. Suckers: growths from the root systems of trees/shrubs, provide meristema&c &ssue e.g. cherries
5. Offsets: small, nearly complete daughter plants produced asexually on the mother plant e.g. tulips
- Gardeners can use these to propagate desirable species asexually, effec&vely and at lower cost than sexual
reproduc&on by taking cuRngs to divide plants into different sec&ons
6.4.2 Producing Cu>ngs
- CuRngs = propaga&on technique to expand plant at low cost whilst guaranteeing desirable characteris&cs
via asexual reproduc&on AND grow to full-size plants much faster than seed-grown plants
- Equipment: scissors, poRng compost, pots for new plants, hormone roo&ng powder, plas&c bag to cover
- Hormone roo&ng powder contains auxins that promote mitosis and cell differen&a&on in new root growth
- If the cut is made just below a stem node, meristem &ssue forms at the lower end of the cut
1. Small length of stem is cut from main plant
2. Base of cuRng is dipped in roo&ng powder
3. Once new roots have started to grow, the cuRng can be planted into soil
6.4.3 Produc:on of Ar:ficial Clones in Plants
Cul:vars
- Natural processes of vegeta&ve propaga&on can form basis of ar&ficial cloning via cuRngs, layering,
gra_ing, division, budding to create cul&vars = strains of gene&cally iden&cal plants that can endure as
foodstuffs or commercial blooms for many years
- All rely on forma&on of meristema&c &ssue from which plant organs can differen&ate
Micropropaga:on and :ssue culture
- Many plant cells are to&potent (can specialise into any type of cell) so a whole plant can be produced from
any of these cells through &ssue culture (ar&ficial growing of cells separate to plant)
- Explant (small piece of plant) is cut -> grown into new clone of original plant
- Used to reproduce endangered species of plant where liAle source material exists
Inves:ga:on
1. Wipe all surfaces with disinfectant and sterilise all apparatus using asep&c technique to avoid fungi
colonising the growth medium and causing micropropaga&on to fail
2. Break off small floret of cauliflower from plant with scalpel, cut a thin sec&on – explant
3. Sterilise explant in disinfectant so only cauliflower cells are present
4. Take out explant with sterilised forceps and add to container of agar growth medium
5. Leave container of agar growth medium and explant on sunny windowsill for 3 weeks
, - Result is to grow a complete cauliflower clone from an explant, showing the cells in the explant have the
capability to produce all different cell types that make up a full cauliflower – hence to&potent
- Complete cauliflower can then be distributed to commercial growers in large numbers
6.4.4 Uses of Plant Cloning
Advantages
1. All plants have same genotype and hence phenotype, gene&c modifica&on allows very dis&nct
characteris&cs to be carried
2. Plants produced are free of disease and can be gene&cally modified to confer immunity to certain diseases
3. Fast process, can yield large numbers of new plants that are small and can be transported easily elsewhere
4. Plants difficult to grow from seed can be produced
5. Can be done in any country in any season
6. Rare and endangered species can be saved from ex&nc&on
7. Prevents risk of F1 hybrids that occur when plants are crossed and grown from seeds = uniform products
Disadvantages
1. Expensive and labour-intensive process
2. Suscep&ble to microbial contamina&on
3. No gene&c varia&on so all offspring are suscep&ble to same diseases/environmental factors -> risk of large-
scale loss of a crop of par&cular plant
4. New plants have to be carefully screened for abnormali&es that could infect new plants
5. Risk of unexpected secondary metabolic chemical reac&on -> causes stunted growth or death in explants
6.4.5 Natural Clones in Animals
Asexual reproduc:on in animals
- Less common than in plants but some small animals produce asexually by parthenogenesis e.g. aphids,
and iden&cal twins can occur
- Iden&cal twins: egg fer&lised by sperm as normal -> forms zygote -> undergoes a few cell cycles ->
becomes an embryo -> splits into two -> forms 2 iden&cal embryos with same genotype -> develop in
utero together -> birth of iden&cal offspring of same gender and iden&cal phenotype
- Non-iden&cal twins are formed from 2 eggs cells and sperm so are not considered clones
6.4.6 Produc:on of Ar:ficial Clones in Animals
Embryo twinning
- Produces offspring that are clones of each other but not of their parents
- Boosts yields of livestock and promotes desirable characteris&cs
- Some&mes embryos are split into 2 single iden&cal cells each implanted into a separate surrogate mother
- Guarantees desirable characteris&cs in offspring but doesn’t predict how many will be produced
1. An embryo is deliberately divided into 2 half embryos
2. Inserted into surrogate mother for gesta&on and birth of iden&cal twins
Reproduc:ve cloning
- Soma&c Cell Nuclear Transfer -> method that produced Dolly the sheep as first livestock created as a clone
- Requires: 1. Animal to be cloned by dona&ng a cell, 2. Female to donate an egg cell, 3. Surrogate mother
1. Animal to be cloned donates a soma&c (body) cell
2. Egg cell is extracted from egg donor and enucleated (removes nucleus and discards)
3. Nucleus from soma&c cell injected into the enucleated egg cell
4. Hybrid zygote cell is treated to encourage it to divide by mitosis
5. Embryo is implanted into the surrogate mother for gesta&on and birth
Therapeu:c cloning
- Uses cloned cells to replace dead/damaged cells that cause loss of func&on in an individual
- Embryos cloned in reproduc&ve cloning, then removed and subdivided
- Each individual embryo cell is a to&potent stem cell that can be cultured and ar&ficially differen&ated ->
can form any specialised cell with the same genome as the sufferer
- Currently lots of poten&al but liAle clinical progress, in the future could help (e.g.) Parkinson’s Disease
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