1. Directional selection and disruptive selection is similar because they both show the distribution of phenotypes. In directional selection the distribution of phenotypes forms a “bell curve.” The selection against one of the phenotypes causes the distribution to “move” in one direction or the other. For example, plants whose flower color is determined by incomplete dominance, colors being red, white, and pink. Pink flowers being the average phenotype, but if the red flower was to be removed from the population, the “mean” phenotype will switch over to the white flowers.
During disruptive selection the average phenotype is selected against. It produces a “2-humped” bell-type curve, the greater distribution is split between the 2 phenotypes. If there was the same type of incomplete dominance with the flowers in the first paragraph, the pink flowers are selected against. Which means that the 2 “humps” shown in the distribution will be centered on the red and white phenotypes. 2. We have always had antibiotic resistant bacteria. It was produced even before humans because we have always had antibiotic. They we just not found out about until scientists discovered them.
An example would be penicillin. This is produces from an antibiotic made by mold. It makes that antibiotic to kill bacteria that would complete for the material mold gets its nutrition from. This is why there is some penicillin resistant bacteria before human developed and discovered it.
When exposing non-resistant bacteria to an antibiotic, most will die. However because of the mutations some of the bacteria may have a resistance to the antibiotic. Bacteria is all subjects to natural selection. Ones that do not have mutations that helps them to survive die. Ones that have mutations survive and pass the mutation on to the next generation.
This same process occurs if the bacteria is exposed to a different antibiotic. That is how some strains of bacteria become multi-antibiotic resistant. 3. Tooth reduction is one of the major evolutionary trends that developed among major vertebrate groups that allowed for the transition from aquatic to terrestrial life. Evolution of limbs and being able to breathe air are other evolutionary trends that took place. 4. In nonvascular plants also some vascular plants reproduce by having the sperm swim through the external environment. Swimming requires a film of water in the external environment, also it requires the ovum to be in a structure close enough to the ground that the sperm can swim to it.
Gymnosperms and angiosperms produce pollen. Sperm are stuck in a pollen grain, so no swimming is required.