Human manipulation of genetic transfer

What this standard asks

• AS 91607 is assessed internally: you research one or more ways people manipulate the passing on of genes, then write a report on how the manipulation works and what it means biologically.
• The manipulations fall into four groups: selective breeding (including embryo selection), whole organism cloning, transgenesis (moving genes between species), and changing how existing genes are expressed, for example by gene editing or gene silencing.
• The implications that earn credit are biological: effects on ecosystems, on genetic diversity, on the health or survival of individuals, on the survival of populations, and on their evolution.
• Social, ethical and economic points can set the scene, but every one should be linked back to a biological effect to count.

Selective breeding

• In selective breeding (artificial selection), people choose which individuals breed, picking those with the traits they want, so the alleles behind those traits become more common each generation.
• Inbreeding (mating close relatives) fixes wanted traits but raises the chance of two copies of a harmful recessive allele; outbreeding (crossing unrelated lines) brings in new alleles and often gives hybrid vigour.
• New Zealand examples: the Perendale sheep was bred at Massey from Cheviot and Romney sheep for hill country; dairy cattle are bred by artificial insemination from bulls chosen by breeding values; and Plant & Food Research bred the SunGold (Gold3) kiwifruit.
• When Psa bacteria reached Bay of Plenty orchards in 2010, the Hort16A gold kiwifruit proved highly susceptible and was largely replaced by Gold3, which tolerates the disease better: breeding both caused and solved a genetic vulnerability.
• Embryo selection is selective breeding at its most precise: in IVF, a cell taken from each embryo can be tested so that only embryos without a serious allele, such as one for cystic fibrosis, are implanted.

Genetic engineering: cutting, pasting and carrying genes

• Restriction enzymes, from bacteria, cut DNA at a specific base sequence (a recognition site); EcoRI cuts at GAATTC, between the G and the A, leaving short single-stranded sticky ends.
• If the donor DNA and a vector are cut with the same enzyme, their sticky ends match by base pairing, and DNA ligase seals the sugar-phosphate backbone to make recombinant DNA.
• Plasmids, small rings of bacterial DNA, are the usual vectors for bacteria; they often carry an antibiotic resistance gene as a marker, so only bacteria that took up the plasmid survive on an antibiotic plate.
• Plants are often transformed with Agrobacterium, a soil bacterium that naturally moves part of its plasmid into plant cells; animals and human cells are often reached with modified viruses.
• PCR copies a chosen stretch of DNA millions of times, and gel electrophoresis separates DNA fragments by size, so the result of each step can be checked.

Transgenesis

• A transgenic organism carries a gene from another species, inserted by genetic engineering.
• Since the 1980s bacteria with the human insulin gene have made the insulin used by people with diabetes, replacing insulin taken from pigs and cattle.
• Bt crops carry a gene from the bacterium Bacillus thuringiensis for a protein toxic to certain insect larvae, so less spray is needed, but pests exposed to the toxin all the time are selected for resistance.
• Golden Rice carries genes that make beta-carotene in the grain, to reduce vitamin A deficiency.
• AgResearch has developed a high-energy ryegrass that grows faster and could cut greenhouse gas from grazing, but because of New Zealand's rules its field trials have been run in the United States.

Try it: which manipulation?

Gene editing with CRISPR-Cas9

• CRISPR-Cas9 uses a short guide RNA, about 20 bases long, that matches the target DNA, and the Cas9 enzyme, which cuts both strands where the guide binds next to a short PAM sequence.
• The cell repairs the cut: end-joining repair often adds or removes a few bases, which can knock a gene out; if a DNA template is supplied, repair can copy it in and make a precise change.
• Unlike transgenesis, an edit can leave no foreign DNA, so the result may be the same as a natural mutation.
• AgResearch edited a coat-colour gene in Holstein-Friesian calves to lighten their black patches, which could help cattle cope with hotter summers.
• Risks include off-target cuts at similar sequences elsewhere in the genome, and mosaic organisms in which only some cells carry the edit.

Try it: change one base and see the protein

Whole organism cloning

• A clone is genetically identical to its parent. Plants are cloned by cuttings, grafting and tissue culture; every Hayward kiwifruit vine, and every vine of a named apple variety, is a clone of one original plant.
• Animals are cloned by splitting early embryos, or by somatic cell nuclear transfer (SCNT): the nucleus of a body cell is put into an egg whose own nucleus was removed, and the egg is stimulated to divide and placed in a surrogate.
• Dolly the sheep (1996) was the first mammal cloned from an adult cell; AgResearch at Ruakura cloned cattle, and like other groups found that many cloned pregnancies failed and some calves were unhealthy.
• Clones give uniform crops and copies of top animals, but a population of clones has no genetic diversity, so one disease or pest can affect them all, as Panama disease is doing to the Cavendish banana worldwide.

Gene therapy

• Gene therapy treats a genetic disorder by adding, replacing or editing genes in a patient's cells.
• Somatic gene therapy changes body cells only, so it affects only the patient; germline therapy would change eggs, sperm or embryos, so the change would pass to future generations.
• Vectors are usually harmless modified viruses: Luxturna uses one to deliver a working copy of a gene to retinal cells in people with an inherited form of blindness.
• Casgevy, approved in 2023, takes a patient's own blood stem cells, uses CRISPR to switch back on the production of fetal haemoglobin, and returns the cells, treating sickle cell disease and beta thalassaemia.
• Germline editing of humans is banned in many countries; in 2018 a scientist in China edited embryos that became twin girls and was imprisoned, because the risks to the children and their descendants were unknown.

New Zealand's rules

• Under the Hazardous Substances and New Organisms (HSNO) Act 1996, any genetically modified organism must be approved by the Environmental Protection Authority (EPA) before it is developed, field tested or released.
• In 2014 the High Court ruled that gene-edited organisms count as genetically modified even when no foreign DNA remains, so they need the same approvals; no genetically modified crops are grown commercially in New Zealand.
• Genetically modified foods must be approved by Food Standards Australia New Zealand and labelled, and gene therapy medicines also need Medsafe approval.
• The Gene Technology Bill, introduced in December 2024 and reported back by Parliament's Health Committee in October 2025, would replace these rules with a Gene Technology Regulator within the EPA and lighter rules for lower-risk edits; it had stalled in Parliament and was not law by late 2026, so check its status when you write your report.
• Decisions must take account of Māori interests: many iwi see genetic modification through whakapapa, mauri and kaitiakitanga, and the EPA has a Māori advisory committee, Ngā Kaihautū Tikanga Taiao.

Biological implications

• Link each implication to a mechanism: what happens to alleles, individuals or populations, and why.