Alleles can disappear from a population through natural selection. This relates to the most fit phenotype because the breed with the desirable trait, or the most fit, will live and produce off spring. Eventually the less desirable trait and its corresponding allele will disappear after multiple generations pass. If the environment does not change alleles of non desirable traits will disappear. <span />
Answer:

Explanation:
Mechanical advantage is given by the ratio of output force by input force.
= Output force = 
= Input force = 
So,

The mechanical advantage of the pulley's is
.
Many scientists agree that the universe is about 13 billion years old.
Answer:
limiting factor whose effects impact a population regardless of the population's density