Human Intervention in Evolution Selective Breeding Selective breeding is an example of artificial selection. In this procedure, only those animals that display a particular trait in their phenotype or are known carriers of the trait are chosen to reproduce. The deliberate selection by a breeder of specific animals to provide the genetic material for the next generation is a process known as selective breeding. This is in contrast to the random mating that occurs when any male animal in a population has an equal chance of mating with any female. Examples of Selective Breeding From early times, artificial selection was carried out to improve herd quality. Farmers selected the best males for mating with their breeding females. In the case of beef cattle, bulls were chosen for their genetic superiority in terms of desirable market characteristics, such as meat yield and non-fatty carcass. For dairy cattle, desirable market characteristics included milk yield and butterfat content. Merino rams are chosen for the fineness (thinness) of their wool fibre and the yield of greasy fleece. Males were also selected based on other inherited features, including good conformation (form, outline or shape), high fertility based on sperm counts and the absence of any known genetic defects. Through artificial selection, farmers could improve the quality of their herds. Problems with artificial selection Artificial selection is in contrast to natural selection that favours only those inherited features that enhance survival and reproduction in the wild. Features that are economically important or aesthetically appealing but that do not contribute to survival and reproduction are not favoured by natural selection and hence are not seen in populations in the wild. Examples of features maintained only by artificial selection can be seen in domesticated animals, such as: – Jacobin pigeons, whose distinctive arrangement of neck feathers forms a ruff that masks their faces, except from immediately in front – hairless cats and dogs – English bulldogs, whose greatly shortened muzzles result in breathing problems Features such as these are only maintained in the gene pool of the populations through human intervention using selective breeding. Reproductive Technologies In commercial herds and flocks, new reproductive technologies associated with selective breeding include: – artificial insemination – sex selection through sperm sorting – multiple ovulation and embryo transfer – oestrus synchronisation Artificial insemination (AI) This technique brought about changes in herd management by altering the ‘how’, ‘when’ and ‘where’ of breeding. AI involves collecting semen from a selected stud animal and then introducing this semen by artificial means into the reproductive tract of females of the same species. When first developed, the technique of AI involved the use of fresh semen only. In 1949, a successful technique was developed for freezing semen.. The freezing technique involves adding semen to a special solution with a controlled pH and which comprises a mixture of various chemicals, including glycerol. Samples of this diluted semen (0.25 mL volume) are taken up in ‘straws’, frozen rapidly and stored in liquid nitrogen at –196°C. Under these circumstances, semen samples can be stored for many years and still retain their ability to fertilise an egg after thawing. Artificial insemination (AI) The use of AI increases the number of offspring that one stud animal could produce. One ejaculate from a male bull contains sufficient sperm to fertilise ten eggs. This volume of semen can be divided into ten portions and used to artificially inseminate ten cows and so can produce ten offspring. In contrast, in a natural one-to-one mating, that same volume of ejaculate would normally produce just one offspring. Through AI technology using frozen semen, physical and temporal barriers to mating are removed. This technology means that one prize stud animal can: – fertilise many more females than under natural conditions – fertilise females located hundreds or thousands of kilometres distant from that stud animal because its frozen sperm can be easily transported over great distances – fertilise female animals and produce offspring long after its death. Genetic impact of AI in animal breeding Through the use of AI technology and the transport of frozen semen, the genetic influence of a small number of stud animals has been greatly extended over time and space. The use of a small number of stud males in a breeding program means that genetic variation is reduced compared with the situation that would exist if random mating occurred. Because stud animals are chosen for their superiority in a limited number of inherited traits, several consequences from the widespread use of a few stud animals may result, for example: – specific alleles of a few selected genes will become predominant in the herd and alternative alleles of the genes concerned will be lost – potentially valuable alleles may be unwittingly lost from the genetic composition of the herd because other inherited features are ignored. Overall, the widespread use of AI using a limited number of stud animals can result in a loss of genetic variation from the genetic composition from that species. This loss of genetic variation may not be immediately noticed. If, however, conditions change (for example, the outbreak of a new disease), the loss of alleles such as those for disease resistance may have significant consequences. Sex selection through sperm sorting Under normal circumstances, a sex ratio of about one male to one female is expected in live born mammals. In the beef industry, however, male calves are preferred because they have more beef (muscle) on their carcasses at a given age than females. In contrast, in the dairy industry, female calves are necessary for milk production. Sex selection is now possible. After semen has been collected from a stud bull, for example, it is possible to treat the semen and separate the sperm with X chromosomes from those with Y chromosomes. Sperm cells are first labelled with a harmless fluorescent dye that binds to DNA. The X chromosome in mammals is larger and contains more DNA than the Y chromosome. As a result, the sperm with X chromosomes fluoresce more brightly than those with Y chromosomes. After labelling, the sperm are then separated into two groups depending on their fluorescence. One group comprises the more brightly fluorescing sperm with X chromosomes and the other group comprises the less brightly fluorescing sperm with Y chromosomes. The use of this sperm separation technique has allowed sex selection to occur on a large scale. Multiple Embryo Transfer in Livestock Multiple ovulation and embryo transfer (MOET) allows highquality cows and ewes to make a much greater than normal contribution to the future generations. Multiple ovulation refers to a process whereby a female receives injections of the follicle-stimulating hormone (FSH) that stimulate her to super-ovulate, or produce multiple eggs. An injection of gonadotrophin-releasing hormone (GnRH) is also given to make all the eggs mature at the same time. Embryo transfer refers to the process through which embryos at day 6 to 7 of development are removed from the reproductive tract of a female and transplanted into the tracts of other females of the same species. These females act as surrogate mothers and carry the embryos to term and give birth. MOET is another example of human intervention in the evolutionary process. Multiple Embryo Transfer in Sheep Process is as follows: – A high-quality donor ewe is treated so that she super-ovulates. – When her eggs are released, they are fertilised, typically through AI with sperm from a selected ram. – Fertilised eggs develop within the ewe’s uterus for about 6 days. – At the end of that time, the embryos are flushed from the ewe’s uterus. – On average, about seven embryos can be collected from a single flush. – These embryos are immediately transferred directly into the uterus of young recipient ewes that will be the surrogate mothers of these embryos. – Embryos not transferred to recipient ewes are frozen in liquid nitrogen and stored for later use. (Frozen embryos can be stored indefinitely.) – The same donor ewe can be used for MOET procedures several times during a breeding season. – Over a normal reproductive lifetime, one ewe might produce 30 eggs. – Multiple ovulation, however, greatly increases this egg output. The advantages of embryo transfer are that genetically important female lines can be multiplied at much faster rates than can occur through normal reproduction and that valuable embryos can be stored. Under conditions of natural selection, this would not be possible. One consequence is that embryo transfer reduces the genetic variability in a flock by restricting the number of breeding ewes. Manipulating breeding cycles It is now possible to synchronise the time of oestrus or sexual receptivity of female farm animals, such as cattle and sheep. Oestrus synchronisation results in all sexually mature females being in oestrus within a predictable and narrow time frame, with the result that the time of fertilisation in a herd or flock, either by AI or natural mating, can be more efficiently managed. Synchronisation is also necessary for MOET procedures so that the intended embryo donor and the recipient surrogate mothers will come into oestrus at the same time. Advantages of synchronisation include: – less time (and hence lower labour costs) needed to test animals to see if they are in oestrus or not – higher fertilisation rates and birth rates – more uniform and manageable crops of calves or lambs, since all young are born within a short period – lower mortality rates because greater oversight of all newborns is possible. Oestrus Synchronisation Oestrus synchronisation can be achieved in a number of ways. One method depends on the fact that the hormone, progesterone, inhibits ovulation by stopping production of another hormone, oestrogen, that is needed to bring female animals into oestrus. By adding an external source of progesterone to female livestock, oestrus production and the associated ovulation are suppressed. When the source of progesterone is simultaneously removed from a group, mature females go into oestrus and ovulate within a short time period. How is this external progesterone delivered? Methods to supply progesterone to farm livestock include: – – – – feeding using a dietary supplement implants under the skin sponges inserted into the vagina CIDRs (controlled internal drug releasing devices) inserted into the vagina. In the case of CIDR (pronounced cee-dar) use in cattle, the insert is left in place for seven days. When the insert with its supply of progesterone is removed, the level of circulating progesterone drops and oestrus begins within three days. Artificial pollination in plants A process similar to AI is used by plant breeders with populations of cultivated plants. In plants, the process is termed artificial pollination. Artificial pollination is another example of human intervention in the evolutionary process. Unlike AI, artificial pollination has been used for centuries (Mendel and his peas) The process of artificial pollination involves: – removal of unripe stamens from the plant to be fertilised – protection of the stigma of the selected female plant from stray pollen – collection of pollen to be used in the artificial pollination – transfer of the donor pollen onto the stigma of the female parent. Artificial pollination using a limited number of plants as the source of pollen may alter the genetic composition of a plant population under cultivation and result in less genetic variation in the population compared with a situation of random mating. Artificial pollination is used in the creation of new plant species. In this case, pollen is collected from one species and it is transferred to the stigma of a second closely related species. Creating new species using artificial pollination in plants One example of this was the creation of a wheat–rye hybrid plant. A wheat species (Triticum turgidum) was artificially pollinated using rye (Secale cereale). The result of this artificial pollination was a new plant species with one set of wheat chromosomes and one set of rye chromosomes. Such a plant would be infertile because its chromosomes could not undergo the normal pairing that occurs during meiosis. By using a specific chemical treatment, a doubling of the chromosome number in the plant cells occurred so that the cells then contained two sets of wheat chromosomes and two sets of rye chromosomes. As a result, the mature plant would be fertile because it could undergo normal meiosis. The new species is known as triticale (triti- from the wheat parent and – cale from the rye parent). This new species combined the desirable genetic qualities of wheat with the inherited hardiness of rye. Rye can grow in cold climates and on low nutrient soils. In contrast, wheat is grown mainly in temperate parts of the world. Triticale is the first artificially created cereal crop to be developed and is grown in a number of countries. Artificial pollination combined with the use of chemical treatment to double the chromosome number in cells accelerates evolution. This technique allows genetic material from two species that would naturally have remained reproductively isolated to be artificially combined Cloning Reproductive technologies, such as artificial insemination and artificial pollination, involve modifications to the sexual reproduction that occurs in animal and plant populations. These technologies restrict the source of sperm or pollen to that from selected animals and plants and use artificial means to transfer the selected sperm and pollen to the reproductive structures of females. In sexual reproduction, two parents contribute equally to the genotype of the new organism. In contrast, other reproductive technologies, such as cloning, involve methods of asexual reproduction in which the genetic information of the new organism comes from one ‘parent’ cell only. Mammals are normally produced through a sexual route, that is, from the fertilisation of an egg by a sperm, with the fertilised egg then developing into a new embryo. However, other techniques exist in which a new mammalian embryo does not arise from a single fertilised egg but from other artificially created cell types. These techniques are typically referred to as ‘cloning’ but it is important to realise that there are different cloning techniques. Cloning techniques are yet another example of how humans can intervene in the evolutionary processes. Embryo Splitting Embryo splitting occurs when the cells of an early embryo are artificially separated. Typically, the embryo is produced through in-vitro fertilisation (IVF) and, using a very fine glass needle, the embryonic cells are separated in the laboratory. Each single cell is then implanted into the uterus of a surrogate female parent where embryonic development continues. As a result, organisms produced through the splitting of one embryo are identical. Embryo splitting has been used for some years in the livestock industry. In cattle, for example, embryo splitting enables the genetic output from one mating of a top bull and a prize cow to be multiplied. Instead of just one calf from such a mating, several calves can be produced using surrogate mothers. Cloning by nuclear transfer Some possibilities exist to manipulate cells and their nuclei. It is possible, for example, to: – remove the nucleus from a cell (when this occurs the cell is said to be enucleated) – transfer the nucleus from one cell to an enucleated cell to form a re-designed nucleated cell – fuse a somatic cell with an enucleated cell The birth of two sheep, Megan and Morag, in 1995 marked a significant scientific milestone. These two sheep were the first mammals ever to be cloned using nuclear transfer technology. Each of these sheep developed from an unfertilised enucleated egg cell that was fused with an embryonic cell that contained its nucleus. In each case, the embryonic cell used came from the culture of one embryonic cell line; as a result, Megan and Morag were identical twins. What about Dolly? Dolly the sheep is the first animal that comes to mind when we talk about cloning? Why was Dolly so special? Dolly was created by nuclear transfer like Megan and Morag, but with one key difference. In Dolly’s case an adult somatic cell was used as the donor rather than embryonic or fetal cells. The arrival of Dolly in 1996 represented the first time that cloning via nuclear transfer using adult somatic cells was successful. The use of adult somatic cells, such as skin cells, to construct new organisms represents remarkable human intervention in the evolutionary processes. Through this means, cells from sterile animals or from animals past their reproductive period, or even dead animals, can provide all the genetic information of new organisms. In nature, the normal evolutionary processes would not allow these events to occur. As a side note - Dolly was named in fun after Dolly Parton, because she was derived from an udder (mammary gland) cell. Other animals cloned by nuclear transfer using adult somatic cells Matilda, the sheep, was the first lamb to be cloned in Australia and was born in April 2000 Suzi and Mayzi were Australia’s first calves to be artificially cloned from the skin cells of a cow fetus. Suzi and Mayzi are identical twins but were born two weeks apart in April 2000. cc (short for carbon copy) was the first cat to be artificially cloned using a cumulus cell from an adult female cat, Rainbow, as announced by a group of American scientists in February 2002. Snuppy, the Afghan hound, was the first dog to be artificially cloned from an ear cell of a 3-yearold Afghan hound, as announced by a group of South Korean scientists in August 2005. Snuppy is short for Seoul National University puppy. Snuppy and his surrogate mother Cloning: the downside The success rate in initiating development of the egg cell after transfer of the donor nucleus is low. For example, in the case of an artificially cloned calf, known as Second Chance, 189 implantations were made into surrogate cows before a pregnancy was achieved. This case, however, was remarkable because the adult cell that provided the donor nucleus came from a 21-year-old Brahman bull called First Chance. This was an extremely old adult cell to use as the starting point for cloning. Because of testicular disease, First Chance had been castrated so that he was sterile when one of his body cells was successfully cloned. The kitten cc, produced by somatic cell cloning, was the only one of 87 embryos implanted into surrogate mothers that survived to term. To get Snuppy, 123 dog embryos were surgically implanted into surrogate females and, of these, only three survived for a significant period, with one dying before birth, one dying soon after birth, and the sole survivor being Snuppy. Dolly was the only live birth from a series of 277 cloned embryos. Clearly, somatic cell cloning is presently far from routine, with less than one per cent of the cloned embryos surviving beyond birth. Cloning: the downside There is evidence that each time a mammalian cell divides, the specialised ‘ends’ of their chromosomes lose some DNA base pairs and become shorter. These ‘ends’, which are known as telomeres, do not carry structural genes. Some scientists suggest that the shortening of the chromosome ends is associated with ageing. One question that has been asked is: Will ageing be more rapid in a cloned animal that originates from an adult cell which already has shortened chromosome ‘ends’ than in a normal organism? The death of Dolly in February 2003 suggested that this may be the case. Six-year-old Dolly was put to sleep because of a deteriorating lung disease and arthritis, unusual conditions for a sheep of Dolly’s age and one that was housed indoors, since sheep can live for about 12 years. The question of possible premature ageing in cloned mammals continues to be explored by scientists. Interestingly, some animals cloned by nuclear transfer from adult somatic cells have shown increased telomere length compared to age-matched controls. How? We don’t know at this stage! Other problems with cloning Apart from our lack of knowledge and the low levels of success, the following are also problems associated with cloning: – – – – – Tumours Genetic defects Overgrowth syndrome Premature aging (genetic age) Massive quantities of human eggs would be required to clone humans – Potential insertion of genes that cause problems – Reduction in adaptability due to decreased genetic variation Attitudes to cloning Public attitudes to animal cloning are mixed. Some people support the concept because they believe that it will benefit people by providing a source of tissues for transplantation or other products. Other people oppose the concept for various reasons, such as their belief that cloning is interfering with nature. When people are questioned about the cloning of human beings, there is a very high level of opposition to it. Some governments, including Australia, have banned experiments directed to producing human clones and leaders of some religious groups have opposed human cloning. The Prohibition of Human Cloning Act 2002, passed by the Australian Parliament in December 2002, bans human cloning. This Act took effect on 16 January 2003. Uses for cloning Replacing organs or other tissues Infertility Replacing a lost child Creating donor people Gene therapy Saving endangered species Reversing the aging process Ethical questions associated with cloning Is cloning ethical for humans? If you had a clone, would it be your child or your delayed twin? What about all the duds? What about creating clones for organs? Who should decide who is cloned? Who should have access to cloning technology – only people with good genes? Who should pay for cloning? Should we be allowed to use this technology to design our children? Who does this genetic information belong to? Should people with genetic diseases be cured? Should they have children? Cloning Plants Cloning of plants can occur both naturally and artificially. Natural cloning occurs through cuttings, runners and suckers. Artificial cloning of plants involves the culturing of a piece of adult plant. As this piece grows, it can be further subdivided so that a large number of genetically identical plants can be produced from the original piece. If large numbers of plants are produced through natural or artificial cloning, the members of the resulting population are genetically identical. As a result, these populations have very limited genetic variation compared with a population that has been produced by sexual reproduction. Bananas are a natural example of plants reproducing by cloning. Having a 3N genome, bananas are unable to successfully undergo meiosis. Transferring genes between species Under normal conditions, genes of one species can be transferred to only another member of that species, for example, from parents to offspring. Transfer of genes between different species normally does not occur. The restrictions that normally prevent gene transfer between different species are known as the ‘species barrier’. These restrictions include the inability of different species to mate and the inability of gametes from one species to fertilise those of another species. Genetic engineering technology, however, has made this species barrier irrelevant. Genetic engineering technology allows the genetic material to be manipulated and enables genes to be transferred between any two species. Examples of these gene transfers include: – the transfer of a human gene into bacteria – the transfer of a human gene into cows – the transfer of a bacterial gene into cotton plants and the transfer of a jellyfish gene into mice. Any organisms that possess a ‘foreign’ gene or segment of ‘foreign’ DNA in their genome as a result of human experimentation are termed transgenic organisms (TGOs). Transferring genes between species The introduction and incorporation of external DNA into a cell can result in permanent genetic changes. – If the cells concerned are prokaryotic cells, such as bacterial cells, they are said to be transformed. – If the cells are eukaryotic cells, when external DNA is added to the cells they are said to be transfected. Various techniques exist for transferring genes into a host cell. These include: – micro-injection of the DNA of a gene into a cell, such as an egg cell or a somatic cell – transfer using a virus, either a retrovirus or an adenovirus, to carry the gene – use of an electric pulse (electroporation) – use of ballistics (the ‘gene gun’) These various techniques are ‘hit-and-miss’. Cloned transgenic animals In the past, when scientists wished to create a genetically modifi ed transgenic mammal, the only method available was microinjection of the DNA of the gene concerned into newly fertilised eggs. The eggs were then implanted into females and the embryos were allowed to develop to term. It was only after the baby mammals were born that they were tested to see if the gene had been taken up. Success rates using this method were not high, perhaps just one in 100. The successful application of artificial cloning to transgenic animals in 1997 has overcome this problem. Soon after development begins, the cells of a transgenic embryo can be artificially separated so that the single cells then develop into a number of identical organisms. Human genes and genes of other species have been engineered into mammalian cells, such as hamster cells and mice cells. Human genes have also been engineered into mammalian clones, such as cattle, sheep and goats. These events are not possible under the normal evolutionary processes. Cloned transgenic animals George and Charlie were the first transgenic cows to be artificially cloned. They were derived from cattle body cells that had been genetically altered to incorporate the human gene for a particular blood protein known as serum albumin. Clint, Arnold and Danny were the first goats to be artificially cloned from adult goat cells. They were also transgenic as their cells contained the spider gene for silk production. Mira, Mira and Mira were three genetically identical female goats produced by artificial cloning of an adult goat cell that incorporated a human gene that controls production of a protein that prevents blood clotting. The milk produced by these goats contains this human protein. Difference between transgenic organisms and genetically modified organisms The term genetically modified organism (GMO) refers to any organism whose genetic makeup has been artificially changed. So, all transgenic organisms are GMOs but not all GMOs are transgenic organisms (TGOs). GMOs include organisms whose genotypes have been modified but the modification does not involve insertion of gene(s) from a different species. Such modifications can include the switching off (or silencing) of a gene that is normally active in an organism. For example, in 2004, an American biotechnology company started taking orders for genetically modified cats to go on sale in 2007. – The gene that will be ‘silenced’ is one that is normally active in cells of a cat’s skin and its salivary glands and it controls production of a protein, known as cat allergen, that is shed by a cat. – Cats engineered to have this gene ‘silenced’ will not produce this protein and, as a result, people who usually suffer from cat allergies will not show allergic symptoms in the presence of these genetically modified cats. Gene therapy Another human intervention that has the potential to change natural evolutionary processes is gene therapy. Gene therapy is a process by which a faulty allele in an organism is replaced by the normally functioning allele of the gene concerned. It is a technique that aims to treat inherited disorders by directly targeting the genotype. This is in contrast to conventional treatments for inherited disorders that act at the level of the phenotype by ameliorating the symptoms of the disorder. Gene therapy provides the prospect for treating inherited disorders for which no treatment presently exists. Gene therapy Technical difficulties must be solved: – How can a gene be targeted to cells of the affected tissue? – How can a gene be targeted to a position where it does not interfere with the function of another essential gene? In addition, ethical issues must be resolved: – Should gene therapy be restricted to somatic tissues only, so that the introduced gene is not transmitted to the next generation? At present, gene therapy affecting germline cells is banned. Before gene therapy is permitted, there must be an assessment of the safety of the patient and the general public and the expected benefit to the patient is compared with the likely risk. At present, gene therapy aims to add copies of the normal allele of a gene into the cells of a target tissue, switching them on to produce the functional protein that is missing in a person with a particular disorder, such as a clotting factor in persons with haemophilia, or a tumour suppression agent in persons suffering from certain cancers. Stem Cells Stem cells are undifferentiated or precursor cells that have the ability to differentiate into many different and specialised cell types, such as nerve cells, blood cells, bone cells, heart cells, skin cells and so on. The first human stem cells were identified in the 1960s and these cells were in the bone marrow One type of stem cell in the bone marrow can differentiate into red blood cells, white blood cells and platelets. Since then, stem cells have been found in other human tissues, such as fat tissue, in skin and in the circulating bloodstream, but in very low numbers. In 1998, scientists discovered how to isolate stem cells from embryonic tissue. Stem cells also exist in other mammalian species and have been widely studied in mice. Because stem cells have the potential to differentiate into specialised cells of various kinds, their potential use to replace faulty or dead cells is great and much research is presently occurring. Stem cells are described as totipotent, pluripotent or multipotent in terms of their power or potency to produce various cell types. Stem Cells Stem Cells In September 2005, scientists at the University of California reported that following the injection of human stem cells from nerve tissue into the spinal cords of paralysed mice, the test group of mice displayed better mobility than the non-injected controls after just nine days and after four months, the test group of mice could walk. The stem cells migrated up the spinal cord and developed into different kinds of cells including those cells that form insulating layers of myelin around nerve cells. Injured spinal cord of mouse following injection of human stem cells. These stem cells developed into myelin-producing cells that form a wrapping (green) around nerve cells (red) (see the areas marked by arrowheads). Other nerve cells remained without a myelin wrapping (see the areas indicated with arrows). Types of Stem Cells Stem cells can also be grouped as follows: embryonic stem cells that – can be obtained from the inner cell mass of an early embryo known as a blastocyst. – A single cell is isolated from the inner cell mass of a blastocyst and is grown in culture, dividing by mitosis to produce a culture of stem cells. – Embryonic stem cells are pluripotent; this means that they can give rise to many different cells types found in a mammal, such as blood cells, skin cells and liver cells. adult stem cells – (more accurately called somatic stem cells) that can be obtained from various sources such as bone marrow, skin and umbilical cord blood – Somatic stem cells are multipotent; this means that they can give rise to certain cell types such as various kinds of blood cells or various kinds of skin cells. Cord blood, for example, contains mainly bloodcell- producing stem cell Therapeutic cloning for stem cell therapy Depending on its purpose, cloning can be separated into reproductive cloning and therapeutic cloning. – Reproductive cloning - purpose of the cloning is to produce a new organism. – Therapeutic cloning – purpose of the cloning is to produce stem cells for use in treatment. Therapeutic cloning involves the creation, through the nuclear transfer technique, of an embryo for the purpose of obtaining stem cells from that embryo. These stem cells are intended for use in treating a patient who has a spinal cord injury or brain injury or has suffered a stroke or has a degenerative disease. Therapeutic cloning for stem cell therapy The cell that provides the nucleus in therapeutic cloning is a healthy cell from the patient who is to receive treatment. As a result, the embryo that is created is a genetic match to the patient and these cells will not cause an immune response. Therapeutic cloning raises possibilities for new treatments for diseases. Application of this technique would mean that normal evolutionary pressures of natural selection will no longer act on people with particular disorders. However, therapeutic cloning also raises major ethical issues. Ethical issues The use of early embryos as a source of stem cells raises many ethical issues since establishing an embryonic stem cell line destroys an embryo. In December 2002, the Research Involving Human Embryos Act 2002 was passed in the Australian Parliament. This Act established a framework that regulated the use of ‘excess’ embryos. An ‘excess’ embryo is one that: – was originally created by artificial reproductive technology for use in IVF procedures, and – has been identified in writing by all ‘responsible people’ as being in excess to the needs of the couple for whom the embryo was first created. Provisions of the Research Involving Human Embryos Act 2002 include the following: – only persons holding a special licence may carry out research on embryos – where that research may damage or destroy the embryo, only excess embryos created before 5 April 2002 may be used – embryos cannot be created solely for research purposes. The provisions of the Research Involving Human Embryos Act 2002 are monitored by the National Health and Medical Research Council (NHMRC) Licensing Committee. Under the provisions of this Act, therapeutic cloning is not permitted in Australia. Genetic screening Genetic screening is a procedure in which a DNA sample is analysed to detect the presence of one or more alleles associated with an inherited disorder. Genetic screening may be carried out as follows: – adult screening, to identify carriers of an inherited disease where a couple wish to determine if one or both of them can transmit an inherited disease to their children – embryo biopsy or pre-implantation genetic screening, in which a single cell is removed from an embryo conceived by IVF to determine that the embryo will not later be affected by certain inherited diseases – pre-natal screening, to identify the genetic status of a fetus where a specific inherited disorder is suspected to be present, using chorionic villus sampling or amniocentesis – predictive screening, to identify persons at risk of developing a late onset disease, such as Huntington disease Technology in human reproduction The development of technology has given humans the ability to manipulate reproduction: These advances fall into two categories: – Those that prevent human conception vasectomy (vas deferens cut and sealed) tubal ligation (fallopian tubes cut and sealed) contraceptive pill intra-uterine device (IUD) condom with spermicide diaphragm with spermicide condom alone (rubber sheath over penis) diaphragm alone (cap over cervix) spermicides alone – Those that assist human conception Donor insemination IVF — in-vitro fertilisation Surrogacy Gamete intrafallopian transfer Intracytoplasmic sperm injection Each of these technologies has varying degrees of effectiveness. Issues associated with assisted reproduction There are social, moral and legal considerations associated with assisted reproduction as these techniques are dealing with the creation of human life. Should we interfere with nature? When does life begin? What should happen to frozen embryos on the death or divorce of the parents? Recent legal issues related to reproductive technologies include questions such as: – Should a woman be allowed to use the frozen sperm of her dead husband? – Should sperm be collected from a dead person because a family makes the request? The law needs to change as the technology changes and debate continues on many of the issues that arise. Points to consider Humans change their environment more than any other species, and knowingly or unknowingly affect, at times, the course of evolution. Biological, cultural and technological evolution are today interrelated through modern practices in agriculture and medicine. In modern medicine, genetic screening, gene therapy and cloning can be viewed as intervening in human evolution, with raises ethical issues.