6.2.1 Cloning

Learning Outcomes Describe the production of natural clones in plants using the example of vegetative propagation. Describe the production of artificial clones of plants from tissue culture. Discuss the advantages and disadvantages of plant cloning in agriculture.

Cloning What? Where? Why? When? How?

Cloning A clone is an individual that has the identical genetic makeup of another individual. Nature has its own ability to produce clones, but the term cloning is used for human intervention in order to produce identical individuals with desired characteristics. Potatoes are natural clones as they develop from one parent plant Identical twins are natural clones as they develop from one fertilised egg cell

Cloning The aim of cloning by human intervention will produce two individuals with identical genetic information... Original parent cell Genetically identical daughter cells

Advantages and Disadvantages of Cloning?

Natural Cloning in Plants Natural cloning is called vegetative propagation Occurs in many species of flowering plants Usually involve perennating organs, which enable plants to survive severe conditions eg runners in strawberries bulbs in bluebells, crocus rhizomes in marram grass stem tubers in potatoes root suckers (basal sprouts) in English Elms

Reproductive Cloning Many plants such as the Buttercup can naturally reproduce asexually which always produces clones of the parent plant. ‘Parent’ plant Roots Stolon (runner) The Buttercup produces stolons (runners) which spread horizontally over the soil. Roots and shoots develop from buds on the stolon, and eventually new independent plants are formed.

Produces more offspring eg for agriculture or GM organisms Reproductive Cloning Produces more offspring eg for agriculture or GM organisms

Vegetative propagation in potatoes

English Elm The English Elm only reproduces by suckering The growth of new trees from the roots or meristem tissue in the trunks As all English Elms are genetically identical they are all susceptible to the fungus, Dutch elm disease

Reproductive Cloning For centuries, gardeners and horticulturalists have exploited this ability of many plants to reproduce asexually. New plants can be grown from older plants by taking cuttings. The use of stem cuttings can be used as an easy method for propagating plants such as Geraniums – this is a form of cloning. 1. Cut stem just below leaf joint 2. Remove leaves from lower stem 3. Place cutting in moist compost 4. Water sparingly 5. Cover with plastic bag

Reproductive Cloning Eventually the cutting produces roots, shoots and new leaves. It will be a clone as it is genetically identical to its parent. parent clone By using this method a large number of identical plants can be produced in a short space of time and for minimal cost.

Reproductive Cloning Leaves can also be used to artificially propagate plants. Begonia plant Begonia plants can be easily grown from detached leaves. 1. Carefully remove a healthy leaf 2. Turn a leaf upside down and then cut across the veins 3. Put the leaf right side up onto moist compost and peg it in place 4. Place the cutting inside a plastic bag 5. Small plants should grow from the cuts (3 months)

Reproductive Cloning Hollyhock Hollyhocks and Phlox can be simply grown from pieces of root placed in moist compost. Cover top of cutting with soil Phlox Piece of root Sloping cut at root base Pot

Questions Explain the advantages and disadvantages of propagating crop plants by cuttings rather than planting seeds (4 marks) Suggest why it is important to describe clones as genetically identical to their parent rather than simply identical – and why this may not always be true (5 marks)

Have a go yourself! Use a non flowering stem Make a slanting cut in the stem Dip in hormone rooting powder Reduce leaves to 2 or 4 Plant in soil (ensure your vessel has sufficient drainage) Keep cutting well watered Cover with a plastic bag for a few days Synoptic Q: rooting powder contains which type of plant hormones?

Artificial Cloning in Plants

Artificial Vegetative propagation It is possible to artificially propagate valuable plants Grafting – a shoot section of a woody stem is joined to a root stock Tissue culture/micropropagation

Grafting

Q: in order for a new plant to be propagated which cells will need to be isolated?

Modern Cloning Techniques Plant Tissue Culture Meristem tissue has the ability to differentiate into any cell type. If meristem tissue is isolated it can develop into a whole new plant. First of all a plant is selected with desirable features, e.g. heavy cropping carrot plant with a good flavour.

Modern Cloning Techniques Plant Tissue Culture Then a carrot with the required characteristics is cut into hundreds of tiny pieces which are sterilised in bleach. The bleach kills any microbes that may infect the pieces of tissue, but does not harm the carrot tissue itself. carrot tissue on nutrient agar Each piece of tissue is placed onto nutrient agar jelly (suitable pH) which has all the nutrients and plant growth hormones needed for healthy growth. The tissue culture is then incubated at a suitable temperature.

Modern Cloning Techniques Plant Tissue Culture Tissue culture can be used to propagate almost any plant. The advantages to commercial growers of this method of plant propagation, far outweigh the disadvantages.

Modern Cloning Techniques Plant Tissue Culture - Summary undifferentiated callus In the right growth conditions (suitable temperature, pH, growth substances) carrot tissue on nutrient agar carrot tissue develops into a callus few days young plants are potted up magnified view of differentiated callus with young shoots and leaves callus tissue has differentiated into embryonic shoots, roots and leaves few days differentiated callus

Micropropagation

Modern Cloning Techniques Disadvantages of Plant Tissue Culture Discuss the disadvantages

Cauliflower cloning practical!

Questions Why is it essential that meristem cells are present in the plant tissues used for any artificial vegetative reproduction method? (2 marks) Suggest an advantage of placing a graft on a tree that produces a particular desirable fruit on to a rootstock of a different tree species

Give an example of a natural clone in animals

Artificial Cloning in Animals

Learning Outcomes Outline the differences between reproductive and non-reproductive cloning.

Cloning in Animals Reproductive cloning Non-reproductive cloning Cloning to produce a whole organism Examples Embryo transplantation Dolly the sheep Non-reproductive cloning Using cloning to produce cells Examples Stem cell research Production of cells, tissues or organs

Reproductive cloning in animals Two methods of artificially cloning animals Splitting embryos for embryo transplantation All offspring are identical to each other but not to the surrogate mothers Nuclear transfer using enucleated eggs Nucleus is taken from a differentiated cell in an adult, and placed into a enucleated egg cell

Embryo Transplants/Embryo Twinning In the agricultural industry, yield and productivity in farm animals is just as important an issue as it is for crop plants. Animal farmers can increase their productivity by rearing more animals and increasing their growth rate. Most importantly, selective breeding allows farmers to rear superior animals with characteristics such as increased milk production and faster growth. Cloning and subsequent embryo transplantation are techniques that can allow farmers to have hardy, productive stock at a relatively low cost and within one generation.

Embryo Transplants/Embryo Twinning Sperm is collected from a superior bull, and a superior, genetically valuable cow is brought into oestrus by injecting her with the hormone prostaglandin.

Embryo Transplants/Embryo Twinning The valuable cow (donor cow) is now injected with FSH and LH to stimulate follicle and egg cell development. Egg cells are recovered from the donor cow and fertilised in the laboratory (in vitro). After a few days any resulting embryos can be screened for their sex and any genetic defects. Some of the recovered embryos may be frozen for future use.

Embryo Transplants/Embryo Twinning The fertilised egg cells each divide into a ball of cells. At such an early stage in their development these cells have not yet become specialised. This means that each cell within the ball of cells has the potential to develop into a new fully formed healthy cow. From one screened embryo (with the desired characteristics) the cells are separated and each one grows into a new embryo. Recipient, less valuable cows are brought into oestrus and the embryos are transferred – two embryos are usually transferred into the uterus of each cow for twinning.

Embryo Transplants /Embryo Twinning The embryos will complete their development within the less valuable cows for the full term of pregnancy and eventual calving. This procedure protects the valuable cows from the risks of pregnancy and increases the number of calves born. This way many superior calves can be born within one generation – improving the farmers productivity, competitiveness and profit figure. All superior calves born this way are cloned individuals.

Embryo Transplants /Embryo Twinning - summary

Fusion Cell Cloning /Somatic Cell Transfer The cloning of animals is generally viewed by gene technologists as a means to improve a particular breed or variety. In 1996, scientists at the Roslin Institute in Scotland created the much-publicised ‘Dolly’ the sheep. nucleus Ewe A enucleated cell Ewe B Dolly was created by removing a nucleus from a mammary gland in a ewe (ewe A). An unfertilised egg cell from another ewe (ewe B) was taken and its nucleus was removed. This cell is then described as ‘enucleated’.

Fusion Cell Cloning (SCNT) The mammary gland nucleus was then introduced into the enucleated egg cell, and the new cell was given a small electric shock to fuse the parts together and start the process of cell division (mitosis). nucleus Ewe A enucleated cell Ewe B fusion of nucleus & cell to form zygote small electric shock to stimulate cell division zygote starts cell division Within a few days of keeping the cell in optimum environmental conditions, the cell started to divide into a ball of cells.

Fusion Cell Cloning(SCNT) nucleus enucleated cell Ewe A Ewe B fusion of nucleus & cell to form zygote zygote divides and embryo develops The ball of cells was then implanted into the uterus of another female sheep (ewe C). Following the normal gestation period of 148 days, Dolly was born. Dolly was therefore a genetic clone of the sheep from which the nucleus was taken (ewe A). When a clone is produced by joining a nucleus from one cell with an enucleated cell from another, it is called fusion cloning or adult cell cloning. dolly grew to be a fully developed adult embryo implanted into uterus of black faced sheep after 148 days dolly was born Ewe C

Fusion Cell Cloning(SCNT) - summary

Dolly the Sheep Dolly the sheep is believed to have suffered from a serious health problem which developed at a relatively early age

Artificial Cloning in animals Advantages Disadvantages Moral and ethical Arguments

Non-reproductive cloning in animals Non-reproductive cloning involves the production of genetically identical cells which has advantages:

Possibilities of non-reproductive cloning Potential future uses include Regeneration of heart tissue following a heart attack Repair of nervous tissue eg in cases of MS Repairing the spinal cord Stem cells taken from the patient to produce the tissues mean that tissue rejection by the immune system is less likely Sometimes known as therapeutic cloning As always there are ethical issues!