Question

1. (i) Discuss the problem of pleiotropy for the evolution of more complex functions. (ii) Discuss how gene duplication could help to solve this problem. (iii) Describe two examples of gene duplication in evolution, making sure to explain the function of the ancestral gene as well as the duplicate(s). (iv) For one of your examples, illustrate your answers to parts (i) and (ii).

Answer 1

(i)  Mutation in a pleiotropic gene may have an effect on several traits simultaneously, due to the gene coding for a product used by a myriad of cells or different targets that have the same signaling function.

(ii) If the underlying gene is duplicated, then each of the two nascent paralogs can break free of these pleiotropic constraints and specialize on a more narrow range of substrates. In this way, gene duplication can resolve adaptive conflicts between competing subfunctions of a pleiotropically constrained single-copy gene.

(iii) Pallister Killian syndrome, where part of the #12 chromosome is duplicated.and creating HOX gene

(iv) PKS is typically caused by the presence of a supernumerary isochromosome composed of the short arms of chromosome 12 resulting in tetrasomy 12p, which is often present in a tissue limited mosaic state. The PKS phenotype has also often been observed in individuals with complete or partial duplications of 12p (trisomy 12p rather than tetrasomy 12p) as the result of an interstitial duplication or unbalanced translocation.

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