In a Punnett square, the letters on the outside typically represent the alleles contributed by each parent in a genetic cross.
- The letters on the top of the square often represent the alleles of one parent (usually the dominant and recessive traits).
- The letters on the side (left) represent the alleles of the other parent.
For example, if one parent has the genotype "Aa" (where "A" is a dominant allele and "a" is a recessive allele), you might put "A" and "a" on the top of the square. If the other parent also has the genotype "Aa," you would place "A" and "a" on the side.
This allows you to visualize all possible combinations of alleles for the offspring, which you fill in by combining the alleles from the top and the side for each box in the square.