1. Compare and contrast directional selection and disruptive selection and provide an example of each.
Directional selection occurs when one of the extreme traits of distribution is eliminated and causes a shift in the frequency. Disruptive selection occurs when the average phenotype is selected against. Both disruptive and directional selection alter the allelic frequencies of a population. For example, the beak length of finches changed due to the food sources that were available. Finches with larger beaks survived because they were able to crack seeds that they could eat. As time went on, insects became plentiful and now finches with smaller beaks were now favored by the directional selection. In disruptive selection, British land snails are found in grasslands, hedgerows and forests. In low-vegetation areas, thrushes feed mainly on snails with dark shells that lack light bands. In forest areas, they feed mainly on snails with light banded shells. Thus, these two different phenotypes are found in these populations.
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2. Many pathogenic bacteria species are becoming resistant to antibiotics. Explain how such adaptations can develop through the process of natural selection. (Hint: Relate this example to the conditions that are necessary for natural selection to occur.)
When a population of bacteria gets exposed to any give antibiotic, most of the bacteria will die. Each time a new generation of bacteria is born they must overcome the antibiotics, which are trying to kill them. Those bacteria that are not killed are stronger than those who died. They are more likely to survive and produce their own offspring bacteria that can overcome antibiotics, too.
3. What are the major evolutionary trends that developed among major vertebrate groups, specifically those that allowed for the transition from aquatic to terrestrial life?
There are several major evolutionary trends that developed among major vertebrate groups, specifically those that allowed for the transition from aquatic to terrestrial life. The trends that developed among major vertebrae groups, include improved respiration and protective and insulating body coverings. The transition from water to land also included changing to more efficient reproductive methods like having a placenta for some animals or egg layers for other animals. Tooth reduction is also a major evolutionary trend.
4. Providing examples, explain how sexual reproduction in plants has evolved to become less dependent on water.
Sexual reproduction in plants has evolved to become less dependent on water. Seeds and pollen have been adapted to avoid desiccation by having specific coatings, which aid in keeping the appropriate amount of moisture in the seed or pollen. Many seeds and pollen do not need water to disperse. They can attach to animals and move where the animals move, or they may be consumed by some animals and excreted in distant locations. Different seeds and pollen can be transported by wind dispersal.
