Effects of biotechnology on biodiversity: HSC Biology Module 6

Analyse each technique's effect on biodiversity (within the species and the ecosystem). Sample answer (key points): Biodiversity is the variety of gene pools within species and the variety of species in ecosystems; escaped transgenic salmon could reduce it. Physical isolation (techniques 1 and 5 - quarantine and inland tanks) prevents transgenic salmon escaping; if they escaped they might have a survival advantage, pass on the transgene, outcompete wild fish and reduce both genetic and species biodiversity. Hormone-induced sex reversal (technique 2) produces sperm carrying only X chromosomes (parents are genetically female), so all offspring are female. Using wild-type eggs (technique 3) prevents inbreeding of transgenic stock and introduces hybrid vigour, preventing accumulation of mutations. Pressure shock (technique 4) blocks meiosis II to produce infertile, triploid offspring, so the transgene cannot be passed on. Together, physical isolation, reproductive control and hybrid vigour protect biodiversity within the salmon population and in ecosystems. Marks: 9 = extensive knowledge of biotechnology, reproduction and biodiversity with scientific analyses of the techniques tied to protecting biodiversity; 7-8 = thorough; 5-6 = sound; 3-4 = some; 1-2 = basic/relevant information. Reference multiple levels of biodiversity and how each technique affects it.

Source: NESA 2021 HSC Biology examination and marking guidelines.

Judge each biotechnology's effect on biodiversity using the table, then give an overall judgement. Sample answer: Biotechnologies can increase, maintain or decrease biodiversity. Artificial insemination generally reduces biodiversity because one male can sire many offspring, lowering the number of bulls passing on genes. Selective breeding reduces biodiversity because only individuals with desired traits breed. Whole-organism cloning reduces biodiversity (clones are genetically identical), but as it is not used commercially in cattle its current impact is small. Transgenic organisms could increase genetic diversity by introducing new genes, but again are not widely used. Hybridisation can increase biodiversity through new gene combinations (or reduce it if hybrids are bred in preference to original breeds). Overall judgement: these biotechnologies have the overall effect of decreasing biodiversity in cattle. Marks: 5 = extensive understanding with relevant references to the table AND an informed judgement; 4 = sound with some references and a suitable judgement; 3 = understanding of the effect on biodiversity; 2 = identifies an effect; 1 = relevant information. Common error: using own examples instead of the table, and linking biotech to the organism rather than to biodiversity.

Source: NESA 2023 HSC Biology examination and marking guidelines.

Link repeated use of one pollen source to reduced genetic diversity over generations. Sample answer: If pollen from one plant is used to artificially pollinate a large number of plants, this leads to many offspring that are genetically similar. Over time, if this is repeated in subsequent generations, it will reduce the genetic diversity of the population. Marks: 2 = explains an outcome of artificial pollination on populations; 1 = some relevant information. The key is showing cause (one pollen source -> similar offspring) and effect (reduced genetic diversity/biodiversity in later generations).

Source: NESA 2022 HSC Biology examination and marking guidelines.

Award 1 mark for each correct, distinct way (any two of the following).

1 mark - monoculture / varietal narrowing. Planting a single high-yielding transgenic or hybrid genotype over a large area means most plants are genetically near-identical, so allelic variation across the crop falls.

1 mark - cloning of elite cultivars. Propagating one cultivar by cuttings or tissue culture (for example Cavendish bananas) produces genetically identical plants, concentrating allele frequencies.

Accept also: replacement of traditional landraces and farmer-saved seed with a few patented varieties. Naming a method without linking it to reduced genetic variation does not earn the mark.

1 mark - definition. Biodiversity is the variety of living things, measured as variation at several levels.

1 mark - the three levels. Genetic diversity (allele variation within a species), species diversity (the number and variety of species in an ecosystem) and ecosystem diversity (the variety of ecosystems in the biosphere).

A response that gives only one level, or confuses genetic with species diversity, caps at 1 mark.

1 mark - the mechanism

Pollen from the GM crop can cross-pollinate a closely related wild plant, so the transgene introgresses (crosses) into the wild population's gene pool.

1 mark - the fitness effect

If the transgene confers an advantage (for example herbicide tolerance), wild plants carrying it may gain a survival/reproductive advantage and increase, potentially creating a hard-to-control "superweed".

1 mark - the biodiversity link

The spreading transgene can swamp locally adapted alleles and reduce the genetic diversity of the wild population, and the advantaged weed may outcompete other species, lowering species diversity.

Full marks need the route (cross-pollination), the selective effect, and an explicit link to a level of biodiversity.

Award up to 4 marks for a genuine comparison (both situations addressed for both features).

Genetic diversity (2 marks). A monoculture of one GM cultivar is genetically uniform - nearly every plant carries the same alleles, so the gene pool is narrow. A diverse population contains many genotypes, so allelic variation across the crop is high.

Resilience to disease (2 marks). Because the monoculture shares the same alleles, a pathogen that overcomes that genotype can destroy the entire crop (for example Cavendish banana and Tropical Race 4). In a diverse population, some genotypes are likely to carry resistance alleles, so the disease spreads more slowly and the population is buffered.

The discriminator is "uniform gene pool, all-or-nothing vulnerability" (monoculture) versus "varied gene pool, resistance present in some plants" (diverse). Describing only one side does not reach full marks.

1 mark - prediction

The frequency of the resistance allele will rise sharply (it could exceed 50 percent), so Bt rice becomes progressively less effective.

1 mark - the selection pressure

The Bt toxin is a strong selective agent: susceptible insects are killed before reproducing, while resistant insects survive.

1 mark - differential reproduction

Surviving resistant insects pass the resistance allele to their offspring, so its frequency increases each generation (directional selection).

1 mark - role of the refuge

With no refuge of non-Bt rice, there are few susceptible insects left to dilute the resistance allele by mating with resistant survivors, so resistance spreads even faster.

A response that predicts the rise but does not name selection / differential survival and reproduction caps at 2 marks.

Award up to 2-3 marks per application (description plus the genetic-diversity link), to a maximum of 5.

Whole genome sequencing for managed breeding (2-3 marks). Sequencing endangered individuals reveals inbreeding, regions of low diversity and disease alleles; breeders then pair animals to maximise allelic (for example MHC) diversity in the offspring. Used in the Tasmanian devil insurance population, this preserves variation that might otherwise be lost from the wild.

Gene / seed banks (cryopreservation) (2-3 marks). Facilities such as the Svalbard Global Seed Vault and San Diego's Frozen Zoo store seeds, tissue or cell lines at very low temperatures. This banks alleles (including from landraces and rare individuals) so the diversity can be restored if a population crashes or a variety is lost.

Accept also assisted reproduction (AI, IVF, embryo transfer, SCNT) maintaining founder diversity in small populations. Each application must be tied explicitly to preserving allele variation, not just "saving the species".

"Evaluate" requires a justified judgement weighing both sides, not two separate descriptions. A Band 6 answer references specific named examples and reaches a defensible conclusion.

Application that reduces biodiversity (2 marks)

Monoculture / varietal consolidation: a few high-yielding transgenic or hybrid cultivars displace landraces and farmer-saved seed, so the agricultural gene pool narrows (for example Bt cotton dominating cotton in India and the United States; clonal Cavendish bananas). Add gene flow of transgenes to wild relatives as a natural-population example.

Application that increases or preserves biodiversity (2 marks)

Conservation biotechnology: whole genome sequencing and managed breeding preserve allelic diversity (Tasmanian devil MHC genes), while cryopreservation banks alleles (Svalbard Seed Vault, Frozen Zoo). These tools retain or restore variation that did not previously have a safeguard.

Justified judgement (2-3 marks)

A supported conclusion: biotechnology accelerates the loss of agricultural genetic diversity (the dominant negative trend) while providing powerful conservation tools for natural populations; the net outcome depends on policy - seed-saving rights, refuge requirements, gene-flow regulation and biobank funding. State the judgement explicitly (for example "net effect is negative for agricultural diversity but the conservation gains are real and growing, so the overall sign is policy-dependent"). Listing features without an explicit judgement caps below full marks.

Target a sequenced response: the benefit, the genetic limitation, then a justified judgement.

Benefit (2 marks)

Propagation by cuttings rapidly produces many individuals from limited stock, creating an ex-situ insurance population safe from catastrophic events such as bushfire (relevant to the Wollemi pine after the 2019-2020 fires). The species is protected from immediate extinction.

Genetic limitation (2 marks)

Cuttings are clones: every propagated plant is genetically identical, so the strategy adds no new genetic diversity. With a uniform gene pool the population has no resistance variation against a novel threat - for example the soil pathogen Phytophthora cinnamomi, which has killed wild Wollemi pines.

Judgement (1-2 marks)

A supported conclusion: cloning is justified as an emergency safeguard against extinction, but because it entrenches genetic uniformity it is not sufficient on its own; it should be paired with banking of any remaining genetic variation and, where possible, sourcing distinct genotypes. A response without an explicit, balanced judgement caps below full marks.