Exam 22: Speciation

Platyfish with spots have an X-linked gene that produces the spots.All platyfish have an autosomal repressor that inhibits the expression of the spot-producing gene.The closely related swordtail lacks both the spot-producing gene and the repressor.In backcrosses between these two species, some hybrids receive the spot-producing gene, but not the repressor.These hybrid individuals should have reduced viability because they often develop malignant tumors due to improper regulation of the expression of the spot-producing gene.What can we conclude?

Which species might be expected to have relatively high speciation rates?

What is the main reason why the Rhagoletis flies that prefer apple and those that prefer hawthorn have not collapsed into a single species?

Refer to the table. Certain populations of a copepod (a planktonic crustacean) may be reproductively isolated, even though females will mate with any male.Here, three females from one of the populations are placed with three males from another population.The diagonals represent crosses made between males and females of the same population.The numbers of offspring produced are listed in the table.Which cross shows reproductive isolation?

Two species of mosquitoes look very much like one another to the extent that trained biologists have difficulty telling them apart.These are thus _______ species.

Speciation rates in flowering plants are

Which scenario would not be considered an example of a prezygotic reproductive isolating mechanism?