1. The primary source of variation within a population is mutation. Give two other sources of variation within a population.
Answer
Meiosis and random fertilisation.
2. What happens to the normal distribution curve in a population, if the two extreme phenotypes are selected for ?
Answer
You would see disruptive selection, as shown below.
3. Describe the difference between allopatric and sympatric speciation.
Answer
Allopatric is where the two groups are geographically isolated, then through mutations and natural selection different species are created. Two groups must evolve and be reproductively separated for sufficient amount of time. Sympatric is where the two groups are not geographically isolated, but there is still reproductive separation, as a result of mutations and natural selection.
4. Three species of a wildflower, goatsbeard, were introduced into the USA from Europe. The plants spread and often lived in similar areas. Some hybrids were produced from time to time but they were sterile. After a while, scientists found two new kinds of goatsbeard. They looked like hybrids but they were not sterile. They could reproduce within their own kind but not with any of the original three species. Explain how the scientists knew that the two new kinds of goatsbeard were new species.
Answer
Can interbreed and produce fertile offspring and cannot interbreed with original species of goatsbeard.
5. Name the type of speciation being observed.
Answer
Sympatric, because no geographical isolation has occurred and the species developed in the same area.
6. The scientists found that these new plants were tetraploid, meaning they had four sets of chromosomes and their gametes were diploid. Explain why the new goatsbeard varieties cannot interbreed with the original species.
Answer
The new goatsbeard varieties produce diploid gametes, whereas the original species produce haploid gametes. When they attempt to interbreed, the resulting offspring would be triploid, and organisms with an odd number of chromosome sets cannot undergo normal meiosis to produce viable gametes. Therefore, the new varieties cannot interbreed successfully with the original species.
7. Suggest and explain how a tetraploid hybrid could be fertile when a normal hybrid was not.
Answer
A tetraploid hybrid has homologous pairs of chromosomes, which allows proper pairing during meiosis. As a result, it can produce diploid gametes. These gametes can then fuse to form a zygote with complete pairs of chromosomes, making the tetraploid hybrid fertile. In contrast, a normal hybrid lacks homologous chromosome pairing, so meiosis cannot proceed correctly and gametes are not viable.