Flexi Says: A Punnett square is a special tool derived from the laws of probability. It is used to predict the possible trait in offspring from a cross between two parents for a single gene and two alleles. But hair color is a complex multiple allele trait that shows epistasis. Epistasis takes place when the action of one gene is modified by one or several other genes. Therefore to predict hair color of offspring from Punnett square is not possible.
