"Isn't it? So basically, there's one sex cell from each parent. Sex cells normally only have one copy of the gene for each trait - " He drew the Punnett's Square on her chest with his fingertips, writing the letters inside each portion. "Each of the two Punnett Square boxes in which the parent genes for a trait are placed actually represents one of the two possible genotypes for a parent sex cell. Which of the two parental copies of a gene is inherited depends on which sex cell is inherited - it's a matter of chance. So I place each of the two copies in its own box, which has the effect of giving it a 50% chance of being inherited." This was all really just an excuse to touch her inappropriately (or actually, Sam thought it was pretty appropriate). "That's still hot, right?"