Sickle cell anemia is known to run in a family. a pedigree chart for this family is shown below. the parents are shown at the top and from left to right appear as a half-shaded circle next to a half shaded square. the two are connected by a straight line. below the parent pair is a vertical straight line connecting the next row of circles and squares which are the offspring. starting from the left an unshaded square, half-shaded circle, another half-shaded circle and a completely shaded square are shown. all these are also connected by a horizontal straight line. what percentage of the offspring have sickle cell anemia? 0% 25% 50% 100%