A mutation is known to disrupt the earliest stages of development in sea urchins. Individuals with two copies of the mutant gene seem to develop normally. When normal males are crossed with mutant (though normal-appearing) females, however, none of the offspring develop at all. How could this pattern of expression be explained?
Babies that were malnourished in utero are at a higher risk for many adult-onset diseases than well-nourished babies. Instead of birth weight to determine how well nourished the fetus was, however, physicians often used the ratio of head circumference to abdominal circumference as a way to detect babies that were malnourished in utero. (In malnourished fetuses, the head circumference to abdominal circumference will be larger than usual because blood in malnourished fetuses is preferentially directed toward the brain.) Why is it better to use the circumference data rather than birth weight data to detect malnourished babies?