Genetic variation and change

Practice

Recall it first, then use it — testing yourself builds the memory, where rereading the notes above only feels easier.

Recall and application shuffled together — you have to work out what each item wants before you can answer it, which is the part the exam actually tests. Both kinds feed the same spacing schedule, so anything you miss comes back sooner.

Say the answer out loud before flipping — that attempt is where the learning happens, even when you get it wrong.

Exam-style only. Instant feedback, shuffled each attempt, best score saved on this device.

What actually comes up

Three questions every year: a Punnett-square cross (Achieved-level genotype/phenotype ratios), then two "discuss" questions drawing from a pool of gene linkage, multiple alleles/co-dominance, lethal alleles, natural/sexual selection, and population genetics (drift, bottleneck, founder effect). At least one population-genetics question — usually built around a real threatened NZ species — has appeared every year.

Across 4 years

The pattern — what to prepare

The 2025 paper ↗ Marking schedule ↗

Question One — Snake genetics

Corn snakes: orange body colour (G) dominant to white (g); striped scale pattern (B) dominant to blotched (b), unlinked genes.

• Cross: homozygous orange+striped × homozygous white+blotched

• a State the gamete genotypes of each parent and the F1 genotype. Achieved
• b Use a Punnett square to show the F1 gametes and all possible F2 genotypes. Achieved
• c Describe the predicted F2 phenotype ratio. Achieved
• d (achieved) Describes linked genes, unlinked genes, crossing over, and segregation. Achieved
• d (merit) Explains crossing over and segregation, how each influences inheritance patterns of linked and unlinked genes, and why the two snake species show different ratios. Merit
• d (excellence) Provides detailed discussion of the inheritance patterns of linked and unlinked genes with reference to the actual snake ratios, confidently linking crossing over and segregation to the observed ratios in each species. Excellence

Question Two — The NZ giraffe weevil / pepeke nguturoa

Male weevils show long- or short-rostrum phenotypes, distributed differently across island and mainland forest habitats, under sexual and natural selection.

• achieved Describes allele frequency, gene pool, migration, genetic drift, natural selection, a selection pressure, population bottleneck, and founder effect. Achieved
• merit Explains migration and genetic drift (allele frequency increasing/fixed or decreasing/lost), their effect on small islands, and natural/sexual selection with a reason each rostrum length succeeds in its environment. Merit
• excellence Provides detailed discussion of how migration and genetic drift changed allele frequencies in the weevil gene pool, and the selection pressures driving natural selection toward the different phenotypes seen in NZ. Excellence

Question Three — Blood types

Human blood type uses multiple alleles (I^A, I^B, i) with co-dominance between I^A and I^B; a pedigree chart shows two children's blood types.

• achieved Describes multiple alleles, the mother's possible genotypes, Child 1's possible genotypes, complete dominance, and co-dominance. Achieved
• merit Explains why Child 1 has two possible genotypes (mentioning gametes from both parents), with a blood-type example each of complete dominance and co-dominance. Merit
• excellence Provides detailed discussion linking co-dominance and complete dominance to Child 1's two possible genotypes, and whether his own genotype could be determined from his children's blood types (using gametes, genotypes and ratios) — and why that determination cannot be guaranteed correct. Excellence

The 2024 paper ↗ Marking schedule ↗

Question One — Cats

Black fur (B) dominant to brown (b); long tail (L) dominant to short (l), unlinked; separately, orange fur is co-dominant and X-linked, producing tortoiseshell females only.

• Cross: homozygous black+long-tail × homozygous brown+short-tail

• a Specify the F1 genotype. Achieved
• b Use a Punnett square to show the F1 gametes and possible F2 genotypes. Achieved
• c Give the expected F2 phenotype ratio. Achieved
• d (achieved) Describes complete dominance, co-dominance, a sex-linked gene, and that females have a homologous XX pair while males have XY. Achieved
• d (merit) Explains why female cats can be tortoiseshell but males cannot, the difference between dominant and recessive sex-linked genes, and why males inherit sex-linked disease more often. Merit
• d (excellence) Discusses the co-dominant and complete-dominance inheritance patterns for fur colour in both sexes, and dominant/recessive sex-linked genes with reference to why males inherit recessive diseases more frequently. Excellence

Question Two — Takahē

Takahē were restricted to a small area during the last ice age, went through a severe bottleneck, and island-translocated populations now show lower genetic variation and fixed alleles.

• achieved Describes population bottleneck, founder effect, genetic drift, gene pool, genetic diversity, a problem from reduced diversity, and a method of future improvement. Achieved
• merit Explains how genetic diversity is impacted by bottleneck, founder effect and genetic drift, why protected island populations still suffer from reduced gene pools and inbreeding, and a realistic way to improve the situation. Merit
• excellence Discusses the impacts of at least TWO of bottleneck, founder effect and genetic drift on genetic diversity, referencing the specific information given about the takahē population. Excellence

Question Three — Lethal alleles in snapdragons

The golden-leaf allele (G) is dominant to green (g), but homozygous dominant (GG) plants die — an aurea × aurea cross gives 2:1, not 3:1.

• a Describe what is meant by the term "lethal allele". Achieved
• b Show a Punnett square for a green × surviving golden-leaf test cross, with genotype and phenotype ratios. Achieved
• c (achieved) Describes both dominant and recessive alleles, that heterozygotes survive, and that lethality can occur later in life. Achieved
• c (merit) Explains how lethal alleles affect expected phenotype ratios, how the test cross shows the lethal allele must be recessive despite dominant colour, and how a dominant lethal allele can exist in and be passed on by an adult. Merit
• c (excellence) Discusses the snapdragon's leaf-colour inheritance using Punnett squares/ratios, and compares the rarity of dominant versus recessive lethal alleles and their existence in adult organisms. Excellence

The 2022 paper ↗ Marking schedule ↗

Question One — Tiger genetics

Orange coat (W) dominant to white (w); striped pattern (S) dominant to no stripe (s), unlinked genes.

• Cross: homozygous orange+striped × homozygous white+no-stripe

• a Identify the genotype of the F1 generation. Achieved
• b Use a Punnett square to show the F1 gametes and all expected F2 genotypes, and give the phenotypic ratios. Achieved
• c Discuss how independent assortment and crossing over affect linked and unlinked genes, and how both affect genetic variation in a population — including a description of linked/unlinked genes, when each process occurs, why linked genes do not independently assort, and a comparison of their effects on variation. Excellence

Question Two — Kākāpō population genetics

Kākāpō crashed from hundreds of thousands to 51 birds by 1995 (50 on Stewart Island, one on the mainland); genome sequencing found the Stewart Island population lost harmful mutations rather than accumulating them, despite 10,000 years of isolation and inbreeding.

• a Discuss possible reasons for the removal of harmful mutations from the Stewart Island kākāpō despite the small population — including what a mutation is and how it enters a gene pool, how natural selection, genetic drift and founder effect may have acted, why harmful mutations may accumulate more in small populations, and three possible reasons for the observed pattern. Excellence

Question Three — Rabbit coat colour

Rabbit coat colour shows multiple alleles (C > c^ch > c) with complete dominance of black over both, and incomplete dominance of chinchilla over albino.

• a Complete monohybrid Punnett squares comparing a black/chinchilla heterozygote cross and a chinchilla/albino heterozygote cross, describing parent genotypes/phenotypes and the resulting genotype/phenotype ratios and pattern of inheritance for each. Achieved
• b Discuss why the genotype ratios are the same for both crosses but the phenotype ratios differ — including complete dominance, incomplete dominance and multiple alleles, and whether each dominance pattern could be an advantage AND a disadvantage to a species, linked to natural selection. Excellence

The 2023 paper ↗ Marking schedule ↗

Question One — Meiosis (budgies)

Green feathers (G) dominant to blue (g); barred wing (B) dominant to clear (b), unlinked genes.

• Cross: homozygous green+barred × homozygous blue+clear

• a State the F1 genotype. Achieved
• b Use a Punnett square to show the F1 gametes and expected F2 genotypes. Achieved

Question Two — Natural selection (human skin colour)

Skin colour is controlled by multiple alleles showing incomplete dominance; melanin protects against UV but UV is also needed for vitamin D.

• a Discuss how human skin colour is a result of natural selection — describing multiple alleles and incomplete dominance, natural selection, why beneficial mutations are retained, and why equatorial vs high-latitude populations differ in skin colour. Excellence

Question Three — Small populations (tara iti)

The tara iti (fairy tern) has fewer than 40 individuals left, with only 8–10 breeding females.

• a Discuss the factors affecting tara iti allele frequencies and genetic variation — allele frequency, genetic variation, and genetic drift; the bottleneck effect and why tara iti exemplify it; how it affects their genetic variation; and how drift affects a small population differently from a large one. Excellence

Grades above are read from each year's own Achievement/Merit/Excellence evidence, condensed to the actual task — the schedules also grade holistically per question on a 0–8 scale, not a fixed mark per bullet.

Past exams & resources

⏱ Timed opens the paper and starts a countdown matching the exam length. Official NZQA PDFs. If a link 404s, that year’s paper may sit under a slightly different code: browse the NZQA subject page.