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36 exam-style questions with model answers, plus 48 quick multi-choice questions — every question on the site for this standard, grouped by the 12 pages of notes they come from.
Write a full answer before you reveal the model one — that comparison is where the marks come from. Every block links back to the notes that teach it.
Define the terms allele, genotype and phenotype. State what is meant by a heterozygous individual.
A population of 200 beetles contains 240 copies of the dark allele and 160 copies of the light allele. Calculate the frequency of the dark allele, and explain why allele frequency is expressed as a proportion rather than as a count.
Two flax plants have identical genotypes for height, but one grows much taller than the other. Discuss how this is possible, and explain the implications for how natural selection acts on a population.
Define mutation, and state the difference between a gametic mutation and a somatic mutation.
Explain why mutation is described as the only source of new alleles, when meiosis also produces genetic variation.
A population of insects is repeatedly sprayed with an insecticide. Within ten years, most of the population is resistant. A farmer concludes that the insecticide caused the insects to mutate so they could survive. Evaluate this conclusion and give a fully correct account.
Name the three processes in meiosis that produce genetic variation, and state how many cells meiosis produces and how their chromosome number compares with the parent cell.
Explain how crossing over produces variation, and explain why it produces a kind of variation that independent assortment cannot.
Some plants can reproduce both sexually and asexually. Discuss the consequences for a population's gene pool of relying on each method, and evaluate which is better for long-term survival.
In pea plants, round seed (R) is dominant to wrinkled (r). Draw a Punnett square for the cross Rr × Rr and state the phenotype ratio of the offspring.
A farmer has a black sheep and wants to know whether it is homozygous or heterozygous for coat colour, where black (B) is dominant to white (b). Explain how a test cross would answer this, and explain what each possible result would mean.
A breeder crosses two heterozygous plants and obtains 100 offspring: 68 tall and 32 short. A colleague argues this disproves the expected 3:1 ratio. Discuss whether the data support or undermine the predicted ratio, and explain what would make the conclusion more secure.
Define incomplete dominance and co-dominance, and give one example of each.
Explain why a cross between two heterozygous individuals gives a 3:1 phenotype ratio under complete dominance but a 1:2:1 phenotype ratio under incomplete dominance.
A researcher studying a NZ plant finds that crossing two flowering plants of the same intermediate colour gives offspring in a 1:2:1 ratio of dark, intermediate and pale flowers. Discuss how the researcher could determine whether this is incomplete dominance or co-dominance, and explain why the distinction matters biologically.
Explain what is meant by multiple alleles, and list the possible genotypes for human blood group A.
Two Manx cats are crossed. Explain why the kittens show a 2:1 ratio of Manx to normal tail rather than the 3:1 ratio a Punnett square would normally predict.
A lethal recessive allele kills homozygous individuals before birth, yet it persists in populations for many generations. Discuss why natural selection does not eliminate it, and compare this with a lethal dominant allele that kills late in life.
List the four types of gamete produced by a plant with the genotype AaBb, and state how many boxes a Punnett square for AaBb × AaBb would contain.
Explain why a cross between two individuals heterozygous for two unlinked genes gives a 9:3:3:1 phenotype ratio.
A researcher crosses two plants heterozygous for two genes and expects a 9:3:3:1 ratio. Instead she obtains 152 offspring in the proportions 9 : 3 : 4 (three phenotypes, not four). Discuss the possible explanations and how she could distinguish between them.
Define linked genes, and state why linked genes do not follow independent assortment.
Explain how crossing over produces recombinant offspring when two genes are linked, and explain why recombinants are less common than parental types.
A geneticist studies three linked genes, A, B and C, on the same chromosome. Test crosses give recombination frequencies of 8% between A and B, 12% between B and C, and 20% between A and C. Discuss what these data reveal, and evaluate the limitations of using recombination frequency in this way.
Explain what is meant by a sex-linked gene, and write the genotype of a female who is a carrier for an X-linked recessive condition.
Explain why X-linked recessive conditions such as red–green colour blindness are far more common in males than in females.
A researcher examines a family tree for a condition that appears in several males across three generations but in no females, and always skips the fathers of affected individuals. Discuss what pattern of inheritance this indicates, how alternative explanations can be ruled out, and what advice could be given to a carrier woman.
Define natural selection, and state what must already be present in a population before natural selection can act.
A bacterial population is treated with an antibiotic. Within months, most of the bacteria are resistant. Explain how this happened.
Many NZ native bird species have declined severely since the arrival of introduced mammalian predators, rather than adapting to them. Discuss why natural selection has not rescued these populations, and what this reveals about the limits of natural selection.
Explain how migration can change the allele frequencies of a population, and state the condition that must be met for it to have any effect.
Two nearby populations of a beetle have very different allele frequencies for wing colour. A new road is built, physically separating them. Explain what will happen to the two gene pools over time.
A conservation manager is deciding whether to translocate kākāpō between two island populations. Discuss the genetic arguments for and against, and evaluate what would make the decision sound.
Define genetic drift, and explain why it has a much greater effect on small populations than on large ones.
Explain the difference between a genetic bottleneck and the founder effect, and explain what both have in common.
Two populations of a NZ skink have the same allele frequencies for a colour gene. One lives on the mainland with 50,000 individuals; the other on a small island with 60. After 50 years, the island population's frequencies have changed dramatically while the mainland's have barely moved. Discuss the likely cause, and evaluate whether natural selection could account for the difference.