A-LevelBiologySelection and evolution9700/42 · Feb/Mar 2017 · Q67 Marks
The Hardy-Weinberg principle may be used to calculate allele and genotype frequencies for a gene, within a population. The Hardy-Weinberg principle uses these equations: p² + 2pq + q2 = 1 p + q = 1
- (a)Within a population of butterflies, the allele for brown wing colour, B, is dominant to the allele for white wing colour, b. 40% of the butterflies in this population are white. Use the Hardy-Weinberg principle to calculate the percentage of butterflies in the population that are heterozygous for the gene controlling wing colour. Show your working. answer %[3]
- (b)Describe four situations where the Hardy-Weinberg principle does not apply.[4]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2017). The mark or mark type is shown in brackets.
- [3] (a) 46.5 - 47 ;;; if answer incorrect allow marks for working q² = 0.4 ; p = 0.368 OR p = 0.37 ;
- [1] (b) four from: 1 mutation;
- [1] (b) 2 migration (into, or out of, the population);
- [1] (b) 3 non-random mating occurs ;
- [1] (b) 4 the population is small;
- [1] (b) 5 selective pressure occurs against one of the, alleles/genotypes ;
- [1] (b) 6 reproduction is asexual;
- [1] (b) 7 organism is haploid;
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