[Campbell Biology P.614] Figure 26.18 illustrates two types of homologous genes. If an ances... | Practice Question

Figure 26.18 illustrates two types of homologous genes. If an ancestral gene in an ancestral species undergoes a speciation event, leading to two distinct species Species A and Species B , and we then compare the homologous gene found in Species A with its counterpart in Species B, what type of homologous gene relationship would this represent, and why?

  • A: Paralogous genes, because they are found in different species due to a gene duplication event.
  • B: Orthologous genes, because their homology is a direct result of a speciation event, meaning the genes diverged along with the species.
  • C: Both orthologous and paralogous genes, depending on whether gene duplication also occurred before or after speciation.
  • D: Homologous genes are only found within the same species, so this scenario is not applicable.

Explanation

Figure 26.18 a specifically illustrates the 'Formation of orthologous genes: a product of speciation'. It shows an ancestral gene in an ancestral species leading to orthologous genes in Species A and Species B after a speciation event. The text defines orthologous genes as those where 'the homology is the result of a speciation event'.