In a Punnett square, which alleles are typically considered dominant?

In the context of a Punnett square, alleles are classified as dominant or recessive based on their expression in the phenotype of an organism. Dominant alleles mask the presence of recessive alleles when both are present in a genotype. In human blood type genetics, the A and B alleles for blood type are both considered dominant over the O allele.

When represented in a Punnett square, if an individual has genotypes containing either A or B alleles, these traits will express themselves in the phenotype regardless of the presence of the O allele. Therefore, the presence of either A or B will result in a characteristic blood type associated with these alleles (type A or type B blood), while type O (which is recessive) requires two O alleles to be expressed phenotypically.

This classification can be demonstrated in a Punnett square where, depending on the combinations of parental alleles, an individual with one A or one B allele will express that phenotype. Thus, in this question, identifying A and B as the dominant alleles correctly represents the understanding of dominance in blood type inheritance and reflects their roles as dominant over the O allele.