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 labeled 1 next to a half-shaded square labeled 2. the two are connected by a straight line. below the parent pair is a vertical straight line connecting to the next row of circles and squares which are the offspring. starting from left an unshaded square labeled 1, half-shaded circle labeled 2, another half-shaded circle labeled 3, and a completely shaded square are shown labeled 4. all of these are also connected by a horizontal straight line. what best describes offspring 4?