Q46 - A Selective Sweep in Cortex Explains Peppered Moth Melanism

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Natural Selection: Modes & Fitness Molecular Evolution & Neutral Theory

The light-coloured form of the English peppered moth (Biston betularia) was replaced by a melanic (dark) form, as camouflaging lichens disappeared due to pollution during the industrial revolution. Clean air, lichens and light moths have now returned. To discover the genetic basis of this, hundreds of moths were genotyped and haplotypes were determined. Melanism was due to a dominant mutation in the cortex gene. Cortex mRNA is cut (spliced) into two forms, Cortex-1A and Cortex-1B. Cortex mRNA abundance was measured.

Figure for Q46: A Selective Sweep in Cortex Explains Peppered Moth Melanism

Using the information and data, determine which of the statements are true or which are false.

A. There is a greater diversity of haplotypes in the population close to the melanic cortex allele, than further away.

B. Cortex-1A is more likely to be driving melanism than Cortex-1B.

C. The expression data are consistent with the melanic phenotype being dominant.

D. The light form has reappeared because of back-mutation (reversion).

← Previous: Q45 Back to Theoretical A →

Question reproduced from IBO 2017, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key & worked solutions