Final answer:
Heterozygous pairs of alleles can sometimes produce an intermediate phenotype, known as incomplete dominance. However, not all heterozygous pairs of alleles exhibit this pattern. It depends on the specific genetic traits and the pattern of inheritance, which can include complete dominance and codominance.
Step-by-step explanation:
The phenotype of heterozygous pairs of alleles can sometimes produce an intermediate phenotype. This is known as incomplete dominance. An example of this is seen in snapdragons, where a cross between a homozygous parent with white flowers (CWCW) and a homozygous parent with red flowers (CRCR) produces offspring with pink flowers (CRCW). In this case, the allele for red flowers is incompletely dominant over the allele for white flowers.
This pattern of inheritance is described as incomplete dominance, denoting the expression of two contrasting alleles such that the individual displays an intermediate phenotype. However, it is important to note that not all heterozygous pairs of alleles produce an intermediate phenotype. In Mendelian genetics, other patterns of inheritance, such as complete dominance and codominance, can occur.
Complete dominance is when the dominant allele completely masks the expression of the recessive allele, resulting in only one phenotype being displayed. Codominance is when both alleles are fully expressed, resulting in both phenotypes being displayed simultaneously. Therefore, the presence of an intermediate phenotype in heterozygotes depends on the specific genetic traits and the pattern of inheritance.