QUESTION 9 (3 marks)
A computer simulation was used to observe genotypic changes in the gene pool of 20 randomly selected rabbits. The simulation was set with these parameters:
• each rabbit’s coat colour was either black or white
• black alleles were dominant; white alleles were recessive
• the number of rabbits was constant in each generation and breeding was random throughout the population
• an environmental factor was chosen in the simulation to provide selection pressure. The table shows the results of the simulation at the start and after 20 generations.
Initial population genotypes | Population genotypes after 20 generations |
BB BB BB BB BB BB Bb Bb Bb Bb Bb Bb Bb Bb Bb Bb bb bb bb bb | BB BB Bb Bb Bb Bb Bb Bb Bb Bb bb bb bb bb bb bb bb bb bb bb |
Contrast the initial allele frequency with the allele frequency after 20 generations to draw a conclusion about the effect of the selection pressure on the rabbit population.
QCAA guide · typeset solution
QCAA sample response and mark allocation
9 | Initial allelic frequencies were B 0.55 and b 0.45. Allelic frequencies after 20 generations were B 0.3 and b 0.7. B decreased (from 0.55 to 0.3) and b increased (from 0.45 to 0.7). This selection pressure was in favour of white rabbits as both genotype and allelic frequencies shifted toward the white phenotype and the white allele. | • provides the correct initial and final allele frequencies [1 mark] • identifies consequentially correct change in allele frequency [1 mark] • states a consequentially valid conclusion [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.