A Punnett square can used to predict the variability of offspring in a certain cross by combining the combining the genotypes of the parents:
The genotype of the parents are written on the top row and on the first column. As an example, for hair texture trait, curly hair is dominant and straight hair is recessive.
One parent has the genotype CC (pure curly haired) while the other parent has the genotype Cc (hybrid curly haired). The Punnett square is shown below. The combination of the genotypes predict the possible offspring.
________________
|____|__C__|__C __|
|_C _|__CC_|_CC__|
|_c__|__Cc_|__Cc__|