Complete dominance in genetics refers to traits that have:

Complete dominance in genetics describes a scenario where one allele completely masks the expression of another allele in a heterozygous individual. This means that when two different alleles are present, the dominant allele’s trait will be expressed, while the recessive allele’s trait will not.

In this context, the correct answer signifies that there are only two forms of a trait: one that is dominant and another that is recessive. For instance, in a typical Mendelian trait, if 'A' represents the dominant allele and 'a' represents the recessive allele, individuals with the genotype 'AA' or 'Aa' will display the dominant trait, while only individuals with the genotype 'aa' will display the recessive trait. This binary interaction between the two alleles is what characterizes complete dominance.

Hence, the correct answer reflects the nature of dominance, where only two forms—dominant and recessive—are involved in determining the phenotype. In contrast, the other options do not accurately capture the essence of complete dominance. Only one form suggests a monogenic trait with no variability, more than two forms indicates incomplete dominance or codominance scenarios, and no dominant form would imply the absence of a clear dominant/recessive distinction, which