Ewe were always on my mind…. Title: Clones in animals Homework: learning package 11 due in today Ewe were always on my mind….

Learning Outcomes (e) describe how artificial clones of animals can be produced; (f) discuss the advantages and disadvantages of cloning animals (HSW4, 6a, 6b, 7c).

Stem Cells All cells start of with the same DNA, so why do they end up looking so different? Some genes “switch on” while others “switch off”, leading to a process called differentiation. Cells that have differentiated cells lose their ability to divide and produce more cells of different kinds.

Stem Cells What happens to cells that remain undifferentiated? These undifferentiated cells are called stem cells – they have the ability to become any other cell in the body (or more stem cells). Why is this useful?

Obtaining stem cells - embryos Most useful at a few days old – ball of undifferentiated cells. Cells at this stage are totipotent – divide to form a whole new organism! 50-100 cell stage is described as pluripotent – ability to become any cell type, but not a new organism because some cell differentiation has already started.

Totipotent cells can divide to form a new organism Stem cells Embryonic stem cells Totipotent cells can divide to form a new organism Pluripotent cells can divide to form any other specialised cells of any type

Embryo formation Embryo is formed by transferring DNA from embryonic stem cells to an egg whose nucleus has been removed (enucleated). Reconstructed egg containing DNA from a donor cell is treated with an electric current to stimulate cell division and blastocyst formation.

Cloning by nuclear transfer

Cloning by splitting embryos

What are the differences between cloning by splitting of embryos and cloning by nuclear transfer? The nucleus comes from an egg fertilised in vitro and allowed to divide to form an embryo The embryos produced are clones of the original zygote The zygote is a product of a fertilised egg. Since this is formed from fusion of sperm and egg cells which are themselves a product of meiosis, it is impossible to know exactly what characteristics the cloned organism will possess All cellular components are derived from the original zygote. The mitochondrial DNA component will be identical in each clone Nuclear transfer The nucleus comes from an adult, differentiated cell taken from the animal to be cloned The embryos produced are clones of the donor adult organism The adult cell is a product of an adult with known characteristics. It is therefore known what characteristics the clones will possess The cellular components are derived from the egg cell used therefore the mitochondrial DNA component will be different from that of the original adult cell

Reproductive vs non-reproductive 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

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

Non-reproductive cloning in animals Non-reproductive cloning involves the production of genetically identical cells 1951 – HeLa cells Cancerous cells which divide repeatedly in culture solution Used in medical research Stem cells Totipotent or pluripotent Undifferentiated cells that are able to differentiate into specialised cells Embryonic stem cells – ethical arguments

Possibilities of non-reproductive cloning Potential future uses include Regeneration of heart tissue following a heart attack Repair of nervous tissue 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

Advantages and disadvantages of cloning animals High-value animals, for example cows giving high milk yield, can be cloned in large numbers High-value animals are not necessarily produced with animal welfare in mind. Some strains of meat-producing chickens have been developed that are unable to walk Rare animals can be cloned to preserve the species As with plants – excessive genetic uniformity in a species makes in unlikely to be able to cope with, or adapt to, changes in the environment Genetically modified animals – for example sheep that produce pharmaceutical chemicals in their milk – can be quickly reproduced It is still unclear whether animals cloned using the nuclear material of adult cells will remain healthy in the long term. Dolly was put down at 6 years old due to lung cancer caused by a virus, although post-mortem showed nothing unusual

Artificial Cloning in animals Advantages High value animals Rare animals can be cloned Quickly reproduced Disadvantages Animal welfare Genetic uniformity, loss of genetic variation Uncertainties of health of cloned animals Moral and ethical Arguments Is it right to clone an aging pet? Is it right to clone an animal which leads to a cure for human diseases?

Give reasons why repairing a damaged heart using cloned cells could potentially be less dangerous than receiving a heart transplant Heart transplant surgery carries with it risk of infection associated with any major surgery. There are also risks associated with use of general anaesthetic. The transplanted heart is foreign tissue – as such it may be rejected by the host’s immune system. Cloned cells are derived from the host and it may be possible to get them to the right location using relatively minor surgical methods