Answer: Hello! xoxo
Upon analysis of the results, a hypothesis can be rejected or modified, but it can never be proven to be correct 100 percent of the time. For example, relativity has been tested many times, so it is generally accepted as true, but there could be an instance, which has not been encountered, where it is not true.
When a single copy of a disease allele doesn't result in a disease but instead is good for the person or organism that carries it, we say that allele has a heterozygote advantage. In other words this occurs when heterozyhotes have increased fitness over both homozygotes. A good example is sickcle cell trait, which protects against malaria in heterozygotes, but causes a deadly disease in homozygotes.
A controlled variable is not changed throughout an experiment. It is there so that the other variables being tested on can be better understood.
