Exam 24: The Origin of Species

The largest unit within which gene flow can readily occur is ________.

A female fly, full of fertilised eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly and their balancing organs (halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap. Fly species W, found in a certain part of the island, produces fertile offspring with species Y. Species W does not produce fertile offspring with species X or Z. If no other species can hybridise, then which of the following statements about species W and Y are true? I. Species W and Y have genomes that are still similar enough for successful meiosis to occur in hybrid flies. II. Species W and Y have more genetic similarity with each other than either did with the other two species. III. Species W and Y may fuse into a single species if their hybrids remain fertile over the course of many generations.

Many songbirds breed in North America in the spring and summer, and then migrate to Central and South America in the autumn. They spend the winter in these warmer areas where they feed and prepare for the spring migration north and another breeding season. Two hypothetical species of sparrow, A and B, overwinter together in mixed flocks in Costa Rica. In spring, species A goes to the east coast of North America, and species B goes to the west coast. What can you say about the isolating mechanisms of these two species?

Which of the following statements describes mechanical isolation prezygotic barrier?

The peppered moth provides a well-known example of natural selection. The light-coloured form of the moth was predominant in England before the Industrial Revolution. In the mid-19th century, a dark-coloured form appeared. The difference is produced by a dominant allele of one gene. By about 1900, approximately 90% of the moths around industrial areas were dark coloured, whereas light-coloured moths were still abundant elsewhere. Apparently, birds could readily find the light moths against the soot-darkened background in industrial areas and, therefore, were eating more light moths. Recently, use of cleaner fuels has greatly reduced soot in the landscape, and the dark-coloured moths have been disappearing. Should the two forms of moths be considered separate species?

A narrow hybrid zone separates the toad species Bombina bombina and Bombina variegata. What is true of those alleles that are unique to the parental species?

Which of these animals could overcome the geographic barrier of water that causes allopatric speciation?