Manipulating genes

Manipulatinggenes © Sir Ralph Riley

2 Cross breeding Ever since humans have been domesticating animals and raising crops they have been (unwittingly) manipulating genes By cross pollination and cross breeding they have tried to introduce the beneficial characteristics of one variety into a different variety of the same species* For example, a bull born to a cow that has a good milk yield, might be mated with a cow from a low-yielding stock, in the hope that the offspring will inherit the characteristics which lead to a high milk yield This has been done for thousands of years without any knowledge of genes or the mechanism of inheritance

3 Crossing In the following (hypothetical) example, a variety of high yielding wheat which has poor resistance to disease… …is crossed with a variety which has good disease resistance but gives a poor yield The gene* for ‘high yield’ is represented by H The gene for ‘low yield’ is represented by h The gene for ‘good disease resistance’ is represented by R The gene for ‘poor disease resistance’ is represented by r

4 pollen grain ovule HHrr high yield low resistance hhRR low yield high resistance The F1 consists of plants with high yield and good resistance zygote

5 Can you see any disadvantages in this method of manipulating genes ? Try working out what would happen if you tried to breed from the F1 Work out the various gene combinations in the gametes Put them into a 4x4 Punnett Square

F1 cross 6 F1 cross HhRr x HhRr Possible combination of genes in gametes HR Hr hR hr HR Hr hR hr HhRR HhRr HR HHRR HHRr HHRr Hr HHrr HhRr Hhrr hR HhRR HhRr hhRR hhRr hr Hhrr hhRr HhRr hhrr The F1 does not breed true. Of the 16 possible combinations of genes, 7 do not have the combined beneficial genes

7 wheat a b c d e Manipulating genes by cross breeding Wheat variety (a) was crossed with wild grass (b) to give hybrid wheat (c) Hybrid wheat (c) was crossed with wild wild grass (d) to give hybrid wheat (e) used for making flour and bread a xb = c c x d = e © Sir Ralph Riley

8 Genetic engineering Interbreeding transfers the complete genome of one variety to another. This means that many new and unpredictable gene combinations may be formed in addition to those intended This method of genetic recombination can take place only between varieties of the same or closely related species Genetic engineering makes it possible to transfer single genes The genes can also be transferred from one species to a totally different species

9 Plasmids There are several ways in which genes from one organism can be inserted into a different organism They can be coated on to microscopic gold particles and ‘fired’ into the cells They can be delivered by viruses They can be transmitted by using structures, called plasmids, present in bacteria For example, the human gene for making insulin can be transferred to bacteria, which are then allowed to reproduce in a culture medium from which the insulin can be extracted

A bacterium 10 in addition to a loop of DNA… …bacteria also contain numerous rings of DNA called plasmids cell wall cytoplasm 0.001mm cell membrane the plasmids can be extracted and used for genetic engineering

11 Inserting a gene plasmid human DNA strand restriction enzyme cuts plasmid the same restriction enzyme cuts the insulin gene out of the human DNA insulin gene the insulin gene is inserted into the plasmid

Recombinant plastids 12 The recombinant plastids are inserted into a bacterium * the insulin gene makes the bacterium produce insulin

Applications 13 Only about 1 in 100,000 bacteria take up the recombined plasmids There are techniques for identifying and isolating these bacteria The bacteria with the insulin gene are then allowed to reproduce in a culture solution from which the insulin can be extracted* Human growth hormone can be made in a similar way Factor VIII, needed by haemophiliacs, (blood clotting disorders) can be produced from hamster cells containing plasmids with the factor VIII genes Chymosin, used for clotting milk in cheese-making, can be produced from yeast cells with recombinant plasmid DNA

Applications 14 As well as producing useful substances from genetically altered cells, whole organisms can be genetically modified. Some examples are …. A bacterial gene which makes an insecticide can be introduced into crop plants, e.g. maize and cotton, to make them resistant to attack by moth caterpillars A gene which confers resistance to herbicides has been inserted into crop plants so that spraying kills weeds but not the crop plants A gene introduced to oilseed rape makes the oil more suitable for commercial processes, e.g. detergent production Genes which control the production of human enzymes have been inserted into sheep so that the enzymes can be recovered from their milk

Applications 15 Genetic engineering does not always have to involve gene transfer between unrelated organisms Genes in a single organism can be modified to improve their characteristics or their products A gene for the production of ß carotene (a precursor of Vitamin A) has been introduced to rice to benefit countries where rice is the staple diet and Vitamin A deficiencies are common* The next slide shows tomatoes which have been genetically modified to suppress production of an enzyme which causes the fruit to soften as it ripens. This improves the keeping qualities

Tomatoes Genetically modified Control tomatoes Genetically modified tomatoes After storage After storage © AstraZeneca

17 Opponents of genetic engineering stripped the bark off these poplars in order to kill them. A gene had been inserted which softened the cell walls so that fewer environmentally damaging chemicals were needed in paper-making.

Cloning 18 When organisms reproduce asexually, all the offspring receive a full set of genes from the parent. As a result they are identical to each other and to the parent Examples are Bacteria and single-celled organisms Plants with vegetative reproduction by bulbs, corms etc. Fungi Some of the lower invertebrates A population of identical individuals arising from asexual reproduction is called a clone

19 Clone of crocuses A clone of crocuses

Bacterial clone Next slide

20 Vertebrates do not reproduce asexually but clones can be produced artificially In some cases this is done by transferring the nucleus from a body cell to an egg cell (ovum) from which the nucleus has been removed The following slide illustrates one of the first successful techniques for cloning a mammal

21 Dolly cells in sheep A’s mammary gland egg cell (ovum) from sheep B diploid nucleus one cell isolated nucleus removed the two cells are fused together * cell division produces early embryo embryo implanted in uterus of sheep C cloned lamb born

22 Sheep, pigs, horses, cows and, by now, probably many more animals have been cloned So far, this is being done on an experimental basis Hundreds of embryos have to be prepared and implanted to obtain one or two successful births If the process becomes cheap and reliable it means that beneficial genes will be present in all the offspring, thus eliminating the chances of their being lost during conventional breeding Before the early embryo is implanted in the surrogate mother, it can be broken up into its individual cells. Each of these can develop into a new embryo

23 fertilised frog egg at the 8-cell stage, any one of these cells can develop into a frog cell division to form an embryo growth and development to produce tadpole and frog

24 Clone of frogs each cell can develop into a frog 8-cell frog embryo cells separated

25 Embryonic stem cells The cells from the 8-cell embryo are called embryonicstem cells…. …because each one can form all the cells and tissues to produce a complete frog After the 16-cell stage, the cells lose this ability and can only produce specialised cells such as blood, bone and nerve cells Cells capable of dividing to produce specialised cells are called stem cells Specialised cells normally lose the power to divide and may have a limited life span The tissues produced by specialised cells usually contain some stem cells which retain the power of division

26 Skin stem cells hair basal layer cells worn away epidermis cells dividing dermis basal cells (skin stem cells) 2mm these stem cells keep dividing and pushing new skin cells to the outside fat layer section through skin

Blood stem cells 27 red cells several types of white cell stem cell in red bone marrow produces …….. platelets

28 Skin stem cells can normally give rise only to skin epidermal cells Bone marrow stem cells can normally give rise only to 6 types of blood cell But embryonic stem cells can produce all the cells of the body Human embryonic stem cells can be obtained from 10 day embryos* These embryonic stem cells can be cultured in a special nutrient solution

29 Human ESCs section through a 10-day human embryo these cells will contribute to the placenta stem cells transferred to culture dish 0.5 mm nutrient medium* stem cells cultured (cloned) these cells will form the embryo (stem cells)

30 All the cells in the body have a full set of genes When the cells become specialised, they lose their ability to divide and many of the genes are ‘switched off’ For example, the genes for producing hydrochloric acid in a stomach cell would not be functional in a skin cell Even though tissues consist mainly of specialised cells, most of them also contain their own stem cells It may become possible to treat stem cells from specialised tissues with hormones and growth factors that cause them to produce a wider range of specialised cells*

Applications of stem cells 31 Most applications of stem cells are in the experimental stage, are undergoing clinical trials or have been tried on very few patients Possibilities are Replacement of damaged tissues such as heart muscle, skin, bone and cartilage Treatment of disease, e.g. diabetes by injecting islet cells into the pancreas; or Parkinson’s disease by injecting nerve stem cells into the brain If the stem cells can be derived from the patient’s own tissue, rejection by the immune system is avoided

Question 1 What are the possible gene combinations in the gametes From genotypesAAbbandaaBB? (a) Ab (b) AB (c) ab (d) aB

Question 2 Which of the following statements is correct? F1 hybrids from cross breeding or cross pollination… (a) …may not be able to reproduce (b) …can contain genes from unrelated species (c) …may contain unwanted gene combinations (d) …may not breed true

Question 3 Genetic engineering can (a) Transfer genes only within a species (b) Transfer single genes between species (c) Create new species (d) Modify a species

Question 4 The bacterial components which can be used to transfer genes are (a) mitochondria (b) DNA (c) plasmids (d) proteins

Question 5 DNA which has been genetically engineered is called… (a) Engineered DNA (b) Hybrid DNA (c) Modified DNA (d) Recombinant DNA

Question 6 Which of the following can be made by genetically engineered bacteria ? • Human insulin (b) Human growth factor (c) Blood-clotting Factor VIII (d) Blood platelets

Question 7 Which of the following could be described as a clone ? • A litter of kittens (b) A clump of daffodils (c) A bacterial culture (d) An F1 hybrid

Question 8 A cell is removed from cow P. An ovum is obtained from cow Q and its nucleus is removed. The cell from P is fused with the enucleated ovum from Q. The combined cell starts to form an embryo which is transplanted into the uterus of Cow R and in due course a calf is born. Which of these cows is the biological parent of the calf? • P (b) Q (c) R (d) The calf does not have a biological parent

Question 9 Which of these statements is correct ? (a) All cells can produce new tissue (b) Only stem cells can produce new tissue (c) Stem cells can divide (d) All cells can divide

Question 10 Embryonic stem cells differ from other stem cells because … • They can produce only one type of tissue (b) They can produce a complete organism (c) They can produce all kinds of cell (d) They cannot be cloned

Answer Correct

Answer Incorrect

Manipulating genes