Use this worksheet to practice finding the genotype of possible offspring. Then, answer questions about the possibility of a specific phenotype (actual characteristic) showing up. Fill in punnett square by putting the father's genotype on one axis and the mother's on the other. Then, fill in the chart with the appropriate letter from each parent. The resulting combinations are the possible outcome for each birth. So, if a combination results with BB, BB, Bb, Bb, every birth would have a 100% chance that brown eyes would show up in the child. However, there would be a 50% chance that the child would have a recessive blue eye gene.