biological consequences, and ethical, social and legal implications, of the use of reproductive cloning technologies, and of genetic screening for inherited conditions

What this dot point is asking

VCAA wants the biological mechanisms of reproductive cloning and genetic screening, plus the ethical, social and legal implications of using them. This is a SAC-friendly bioethics topic.

The answer

Reproductive cloning

Reproductive cloning produces a new organism that is genetically identical to an existing one. There are two main approaches:

1. Embryo splitting. A very early embryo (at the 2 to 8 cell stage) is mechanically divided into two or more pieces. Each piece, still composed of pluripotent cells, develops into a complete organism. The clones are genetically identical to each other (and to the original zygote) but their genomes came from the natural fertilisation, not from an existing adult. This is essentially artificially induced identical twinning.

2. Somatic cell nuclear transfer (SCNT). The technique used to produce Dolly the sheep in 1996.

Steps:

1. A somatic (body) cell is collected from the adult to be cloned. The cell nucleus contains the full diploid genome.
2. An unfertilised egg is taken from a second adult. Its nucleus is removed (enucleation), leaving a cytoplasm full of maternal factors but no DNA.
3. The donor somatic cell is fused with the enucleated egg using an electrical pulse. The egg cytoplasm reprogrammes the donor nucleus to behave like an embryonic nucleus.
4. The reconstructed cell is activated (often by another electrical pulse) to begin dividing as an embryo.
5. After 5 to 7 days, the embryo (now a blastocyst) is implanted into a surrogate mother to develop to term.

The clone is genetically identical to the donor of the somatic cell (apart from a tiny amount of mtDNA from the egg donor).

Biological consequences of reproductive cloning

• Low success rate. Dolly required 277 SCNT attempts for one live birth. Other cloned species (mice, cats, pigs, horses, dogs) have similarly low success.
• Health problems. Cloned animals often have shortened telomeres, immune problems, premature ageing, organ abnormalities and obesity, partly because the donor nucleus carries the epigenetic state of an adult cell and is incompletely reprogrammed.
• Genetic uniformity. A population of clones lacks genetic diversity, making it vulnerable to disease and environmental change.
• No predictability of behaviour or appearance. A clone shares the genome but environment, epigenetics and stochastic development still shape the phenotype. Cloned dogs and cats do not look or behave identical to their originals.
• Mitochondrial DNA. The clone inherits mtDNA from the egg donor, not the nucleus donor; so it is not a 100% genetic copy.

Applications of reproductive cloning

• Agriculture. Producing many copies of a particularly productive cow, sheep or pig. Used commercially in some countries.
• Conservation. Cloning endangered species (gaur, banteng, black-footed ferret). The Pyrenean ibex was briefly resurrected in 2009 (the cloned newborn died of lung defects).
• Preserving valued individuals. Cloning a beloved pet or a champion racehorse.
• Research. Generating genetically identical experimental animals.

Ethical, social and legal implications of cloning

Animal welfare: the high failure rate, miscarriages, malformed births and shortened lifespans raise welfare concerns.

Human reproductive cloning: widely banned and considered unethical because of safety (the failure rates seen in animals), identity (the clone's autonomy and right to genetic uniqueness), and exploitation concerns. Banned in Australia under the Prohibition of Human Cloning for Reproduction Act 2002.

Therapeutic cloning (creating embryos for stem cells, not for live birth) is more accepted but still raises ethical debate about the moral status of the embryo. Regulated in Australia under the Research Involving Human Embryos Act 2002.

Diversity vs uniformity: cloning reduces genetic diversity, which is biologically risky for populations.

Commercial pressures: patent rights over cloned animals and proprietary techniques raise legal questions of ownership of life.

Genetic screening

Genetic screening is the testing of individuals or populations for specific genetic conditions or carrier status. It has several forms:

1. Prenatal screening. Testing the foetus during pregnancy.

• Non-invasive prenatal testing (NIPT). Sequences fetal DNA fragments circulating in the mother's blood from about 10 weeks. Detects trisomy 21, 18, 13 and sex-chromosome aneuploidies. No miscarriage risk.
• Chorionic villus sampling (CVS). Tissue from the placenta is taken at 10 to 13 weeks. Provides a karyotype and DNA. About 1% miscarriage risk.
• Amniocentesis. Amniotic fluid sampled at 15 to 20 weeks; fetal cells provide a karyotype and DNA. About 0.5 to 1% miscarriage risk.

Prenatal screening identifies conditions such as Down syndrome, neural tube defects (combined with ultrasound), and specific single-gene disorders. Parents use the information for reproductive decisions.

2. Pre-implantation genetic diagnosis (PGD). Embryos created by IVF are tested at the 8-cell stage. Unaffected embryos are implanted. Used by couples at high risk of passing on a serious inherited condition.

3. Newborn screening. A heel-prick blood sample taken from newborns. In Australia, the test screens for around 30 treatable conditions, including:

• Phenylketonuria (PKU). Treated with a low-phenylalanine diet.
• Congenital hypothyroidism. Treated with thyroid hormone.
• Cystic fibrosis. Allows early management.
• Sickle cell disease.
• Galactosaemia, MCAD deficiency, and others.

Early detection allows treatment before symptoms develop.

4. Carrier screening. Tests adults for heterozygous carrier status of recessive disorders.

• Population-based screening for high-risk groups: cystic fibrosis (white populations), Tay-Sachs (Ashkenazi Jewish), beta-thalassaemia (Mediterranean), sickle cell (West African).
• Pre-conception counselling. Identifies couples at risk of having affected children, who can then choose options (natural pregnancy with prenatal testing, PGD, donor gametes, adoption).

5. Predictive testing. Testing healthy adults for late-onset diseases such as Huntington's disease, BRCA1/2 (breast and ovarian cancer risk), or familial cancers. Raises issues about how to act on the information.

Ethical, social and legal implications of genetic screening

Informed consent. Patients should understand what the test reveals, its accuracy, and what options follow. Genetic counsellors are central.

Confidentiality. Genetic information about one person also reveals information about relatives. Family members may not want this information.

Discrimination. Insurance companies and employers could discriminate based on genetic information. Australia restricts insurer use of genetic results from research and certain predictive tests under a 2019 moratorium; legislation remains debated.

Selective abortion. Parents may choose to terminate pregnancies after a prenatal diagnosis of conditions such as Down syndrome. This raises difficult questions about disability, eugenics and choice.

Psychological impact. Knowing one carries a Huntington's allele, with no treatment available, can be distressing. Many at-risk individuals choose not to be tested.

Cost and access. Screening should be available to all who could benefit, not just those who can pay.

Designer babies. PGD for medical conditions is widely accepted; PGD for sex selection or non-medical traits is more controversial and legally restricted in many countries.

Worked example

A couple is planning to have children. Both have a family history of cystic fibrosis (autosomal recessive). They undergo carrier screening and learn they are both heterozygous carriers (Cf/c). Each pregnancy has a 1/4 chance of being affected. Their options include: natural conception with prenatal screening (CVS or amniocentesis) to detect affected pregnancies; pre-implantation genetic diagnosis (PGD) to select unaffected embryos via IVF; using a donor sperm or egg; adoption; or accepting the 1/4 risk. A genetic counsellor helps them weigh the medical, ethical and social factors, including the difficulty of decisions about an affected pregnancy.

Common traps

Saying a clone is "identical". A clone is genetically nearly identical (mtDNA differs) but environmental, epigenetic and developmental noise means clones are not behaviourally or even physically identical.

Confusing reproductive cloning with therapeutic cloning. Reproductive: aimed at producing a live animal. Therapeutic: aimed at producing patient-specific stem cells, never carried to term.

Treating Dolly as an easy success. Dolly took 277 attempts and died younger than typical of her breed. The technology is far from routine.

Saying genetic screening means abortion. Screening provides information. Parents and patients use it in many ways, including preparation, treatment, IVF with PGD or termination.

Forgetting confidentiality issues. Genetic results have implications for relatives, who have not consented to be informed.

In one sentence

Reproductive cloning (especially somatic cell nuclear transfer, which produced Dolly by fusing an adult somatic cell nucleus with an enucleated egg) creates genetically near-identical organisms but with low success, health problems and ethical objections, while genetic screening (prenatal NIPT, CVS, amniocentesis; newborn heel-prick tests; adult carrier or predictive testing) identifies inherited conditions or carrier status, supporting informed reproductive and medical decisions but raising issues of consent, confidentiality, discrimination and the social meaning of disability.