NCEA Level 1 Biology 92022 Genetic variation: past papers, practice and marking
- NCEA Level 1
- Biology
- AS92022
- 5 credits
- External exam
About 92022
AS92022, Demonstrate understanding of genetic variation in relation to an identified characteristic. Chromosomes, DNA, genes and alleles and how they fit together, genotype and phenotype, heritable and non-heritable variation, mutation in gametes and body cells, how meiosis and fertilisation make every offspring different, Punnett squares and pedigree charts, DNA profiling, DNA sequencing and genetic markers, and how small populations, survival, migration and mate choice change allele frequency: the 5-credit external, in the six question types it keeps reusing.
What 92022 covers
- Genes and allelesDefine and use chromosome, DNA, gene, allele, genotype, phenotype, homozygous, heterozygous, dominant, recessive and carrier, explain how chromosomes, DNA, genes and alleles are related with a clear example, and tell heritable from non-heritable variation
- MutationA mutation is a change in the DNA base sequence that makes a new allele, gametic mutations are passed on and somatic (body cell) mutations are not, and a new allele can be harmful, neutral or beneficial depending on the environment
- MeiosisMeiosis makes genetically different gametes with half the chromosomes, independent assortment and crossing over give new combinations of alleles, random fertilisation joins two gametes, each parent passes on one allele by chance, and why siblings differ
- InheritanceComplete a single-gene Punnett square with complete dominance, give genotype and phenotype ratios and probabilities, read a pedigree chart, deduce and justify genotypes from parents and offspring, and say when a genotype cannot be confirmed
- DNA profilingDNA profiling to find a parent, DNA sequencing to find a mutant allele or a carrier, genetic markers to tell how closely related individuals are, the purpose of tracking an allele, and evaluating what the findings do and do not show
- VariationPopulation and allele frequency, how a small population, differing survival, migration and non-random mating change allele frequency, why a recessive allele stays hidden in carriers, and why genetic variation matters for survival
92022 past papers
Open a 92022 past paper beside your own Ako page, then get it marked, part by part.
Work through a past paper All NCEA Level 1 Biology past papers
Practice questions
Question 1: Genes and alleles
Hair colour in humans is affected by several genes. One of them, the MC1R gene on chromosome 16, codes for a protein in the cells that make hair pigment. In this question, the allele for non-red hair (R) is dominant over the allele for red hair (r).
- Define the terms genotype and phenotype.(up to Achieved)
- Give the possible genotypes of a person with red hair and of a person without red hair.(up to Achieved)
- Explain how two parents who do not have red hair can have a child with red hair.(up to Merit)
Check your answer
Part a: what gets the marks
- The genotype is the pair of alleles a person has for a gene, and the phenotype is the characteristic that shows, such as hair colour.
A full answer: The genotype is the pair of alleles a person has for a gene, such as Rr. The phenotype is the characteristic that shows, such as red hair.
Part b: what gets the marks
- A person with red hair is rr; a person without red hair is RR or Rr.
A full answer: Red hair: rr. Not red: RR or Rr.
Part c: what gets the marks
- Both parents must be Rr, so each can pass an r allele to the child, and a child who gets r from both is rr with red hair: a 25% (1 in 4) chance for each child.
A full answer: Both parents must be Rr (carriers): R masks r, so neither has red hair. Each parent passes one allele to the child, and if both pass r the child is rr and has red hair. For each child the chance is 25% (1 in 4).
What gets each grade
Question 2: Genes and alleles
Albinism is a characteristic in which the body makes little or no melanin, the pigment that colours skin, hair and eyes. In the form described here, the TYR gene codes for an enzyme needed to make melanin. The allele for normal pigment (A) is dominant to the allele for albinism (a).
- Describe what is meant by genotype and by phenotype.(up to Achieved)
- Give the three possible genotypes for the TYR gene. For each, state whether it is homozygous or heterozygous and give the phenotype.(up to Achieved)
Check your answer
Part a: what gets the marks
- The genotype is the pair of alleles an individual has for a gene, for example Aa.
- The phenotype is the observable characteristic, for example normal pigment or albinism.
A full answer: The genotype is the pair of alleles an individual has for a gene, for example Aa. The phenotype is the characteristic that can be observed, for example normal pigment or albinism. The phenotype is produced by the genotype and can also be affected by the environment.
Part b: what gets the marks
- AA is homozygous dominant, and the person has normal pigment.
- Aa is heterozygous, and the person has normal pigment but is a carrier.
- aa is homozygous recessive, and the person has albinism.
A full answer: AA: homozygous (dominant), normal pigment.
Aa: heterozygous, normal pigment.
aa: homozygous (recessive), albinism.
What gets each grade
Question 3: Genes and alleles
PKU is caused by the recessive allele (p) of the PAH gene; the normal allele (P) is dominant. In Aotearoa New Zealand every newborn has a heel-prick test for PKU. A baby with PKU who eats a diet very low in phenylalanine from birth grows up healthy.
- Explain the difference between genotype and phenotype, using the three possible genotypes for the PAH gene.(up to Merit)
- Explain why a person with PKU who follows the diet and is healthy still has the genotype pp.(up to Merit)
Check your answer
Part a: what gets the marks
- The genotype is the pair of alleles a person has: PP, Pp or pp.
- The phenotype is the characteristic that shows: PP and Pp people do not have PKU, pp people have PKU.
- PP and Pp give the same phenotype because the dominant P allele masks the recessive p allele, so a Pp person is a healthy carrier.
A full answer: The genotype is the pair of alleles a person has for a gene: PP, Pp or pp. The phenotype is the characteristic that shows. PP and Pp people do not have PKU, because P is dominant and masks p, so Pp people are healthy carriers. Only pp people have PKU.
Part b: what gets the marks
- The diet is an environmental factor that changes the phenotype (no harm from phenylalanine) but does not change the base sequence of the PAH alleles, so the genotype stays pp and can still be passed on.
A full answer: The diet is part of the environment. It changes the phenotype, because phenylalanine no longer builds up, but it does not change the DNA. Both of the person's PAH alleles are still p, so the genotype is still pp, and the p allele can still be passed to their children.