In humans, hemophilia is a sex-linked trait. Females can be normal, have the disease, or to be carriers cor the trait. Males will either have the disease or not, but they won't ever be carriers. Cross of a man who has hemophilia with a woman who is a carrier.

What is the probability that their children will have diseases?

a- all cells come from pre-existing cells

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.