Evaluate the effects of biotechnology on the genetic diversity of agricultural and natural populations, and the impact on biodiversity

What this dot point is asking

NESA wants you to evaluate, not just describe, the effect of biotechnology on biodiversity. Cover both agricultural and natural populations, give specific named examples for each side of the argument, and end with a justified judgement.

The answer

Biodiversity has three levels: genetic diversity within species, species diversity within ecosystems, and ecosystem diversity within the biosphere. Biotechnology affects all three.

Negative effects on agricultural biodiversity

Monoculture and varietal narrowing. Industrial agriculture promotes a small number of high-yielding transgenic or hybrid varieties. The result is genetic uniformity across large areas:

• Bt cotton accounts for more than 90 percent of cotton in India and the United States.
• Most commercial Cavendish bananas are genetic clones, leaving the crop highly vulnerable to Tropical Race 4 of Panama disease.
• Holstein dairy cattle worldwide trace much of their genetics to fewer than 100 elite sires.

Loss of landraces. Patented seed and standardised varieties displace farmer-saved seed and traditional landraces, eroding the genetic base from which future crops will be bred. The Mexican maize landrace decline is a documented case.

Cloning narrows livestock pools. Reproductive cloning of high-value bulls and racehorses concentrates allele frequencies still further.

Negative effects on natural biodiversity

Gene flow to wild relatives

Transgenes can introgress from crops into wild populations via cross-pollination, especially in canola, sunflower and rice. The escaped genes can either swamp local adaptation or, if they confer fitness, create "superweeds."

Non-target organisms

Bt toxin is generally specific to Lepidoptera, but some studies show effects on non-target butterflies (Monarch caterpillars on milkweed exposed to Bt corn pollen). Recent meta-analyses suggest the net effect on non-target arthropods is small or positive due to reduced spraying.

Resistance evolution

Glyphosate-tolerant crops have selected for glyphosate-resistant weeds (Palmer amaranth, horseweed). Bollworm resistance to Bt has emerged in India and the United States. Resistance management requires refuges, crop rotation and rotation of modes of action.

Positive effects: conservation biotechnology

Whole genome sequencing

Sequences of endangered species identify the level of inbreeding, regions of low diversity and disease alleles. Used in the Tasmanian devil insurance population to manage devil facial tumour disease and in the kakapo recovery programme.

Assisted reproduction

Artificial insemination, in vitro fertilisation, embryo transfer and somatic cell nuclear transfer maintain populations of critically endangered species. The northern white rhino is being preserved through oocyte collection and IVF.

Gene and seed banks

The Svalbard Global Seed Vault stores more than one million plant accessions. The Frozen Zoo at San Diego cryopreserves cell lines from over 10,000 animals. The Australian PlantBank holds seeds and tissue cultures of native flora.

De-extinction and genetic rescue

CRISPR allows the introduction of lost alleles into living relatives. The Colossal Mammoth Project aims to edit Asian elephant cells with mammoth alleles. The thylacine project in Australia (Colossal and University of Melbourne) aims to use dunnart cells. Genetic rescue has been used in Florida panthers and black-footed ferrets.

Reduced land conversion (land sparing)

Higher per-hectare yields from biotechnology can reduce pressure to clear new habitat, indirectly protecting biodiversity. The strength of this effect is debated.

Summary table

Evaluation

Biotechnology's effect on biodiversity is split:

• Agricultural genetic diversity is on a clear downward trend driven by varietal consolidation and patented seed. This is the dominant negative impact.
• Natural genetic diversity receives mixed effects. Gene flow and resistance evolution are real concerns; conservation applications partially offset these.

The most defensible judgement is that biotechnology accelerates the loss of agricultural genetic diversity while providing important conservation tools that did not previously exist. The net outcome depends heavily on policy choices: seed-saving rights, refuge requirements, biobank funding and gene-flow regulation.

Examples in context

Example 1. Tasmanian devil insurance population and DFTD. Devil Facial Tumour Disease has reduced wild Tasmanian devil (Sarcophilus harrisii) populations by more than 80 percent since 1996. Save the Tasmanian Devil Program uses biotechnology to maintain a genetically diverse insurance population at zoos including Sydney's Taronga. Researchers sequence individual devils' MHC genes (responsible for immune recognition) and selectively breed pairs to maximise allelic diversity, since DFTD spreads partly because wild devils have very low MHC variation. By preserving over 250 captive animals with curated genetics, the program preserves variation that may otherwise vanish from the wild, ready to be reintroduced as immune-competent founder populations.

Example 2. Wollemi pine clonality and disease risk. The Wollemi pine (Wollemia nobilis), rediscovered in 1994 in Wollemi National Park west of Sydney, exists as fewer than 100 mature wild trees and shows extremely low genetic diversity (almost identical at all sequenced loci, suggesting recent clonal reproduction). Botanic gardens around the world propagate the species by cuttings, which produces genetically identical plants. While this safeguards the species against extinction by fire (catastrophic in 2019-2020), it offers no resistance variation against the introduced soil pathogen Phytophthora cinnamomi, which has already killed wild Wollemi pines. Biotechnology has paradoxically both saved and entrenched the genetic uniformity of this living fossil.

Try this

Q1. Identify two ways biotechnology can reduce genetic diversity in agricultural crops. [2 marks]

• Cue. Monoculture planting of a single genotype, cloning of elite cultivars, and replacement of traditional landraces with patented varieties.

Q2. In a fictional rice variety, a Bt resistance allele appears in 2 percent of an insect population after 5 years of Bt rice cultivation. Predict how this frequency will change over the next 10 years if no refuge crop is planted, and explain the mechanism. [3 marks]

• Cue. Frequency will rise sharply (potentially to over 50 percent) under strong directional selection because Bt-susceptible insects are killed and only resistant alleles reproduce.

Q3. Evaluate the impact of biotechnology on biodiversity. (a) Describe one application that reduces biodiversity. (b) Describe one application that increases or preserves biodiversity. (c) Justify whether the net global effect is positive or negative. [2+2+3 marks]

• Cue. (a) Monoculture or gene flow to wild relatives. (b) Cryopreservation of seed at Svalbard or selective breeding for Tasmanian devil MHC diversity. (c) A judgement that links to policy: regulation determines whether technologies erode or protect diversity.