As you hike up a mountain, you realize that the plants and animals present at the base are not the same as those at the top. this observation is basis of?

This observation in the basis of change in habitat or ecosystem.

Explanation:

At the base of a mountain, we'll most probably find more plants and animals. There will even be trees at the base of mountain. As we move up, there will be a climate change and a change in habitat and ecosystem. There will no trees, fewer number of plants and animals as we go on top of the mountain. All these changes depict that the climate changes the habitat of particular organisms hence, the ecosystem changes.

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.