hypothetically, what if the homozygous form has a side effect, lets say, it makes cell division impossible? then the only way to prove it (apart from maybe things you can do in a biotech laboratory) would be to show statistically that these pairings produce 66.6% pinstripes, instead of the expected 75%. since its only an 8.4% difference between the two values, you would need an awful lot of clutches and eggs to prove that one out.