Incomplete inheritance, also known as partial dominance, is a genetic concept where neither allele in a pair is completely dominant over the other. This results in a phenotype that is a blend or intermediate of the two parental traits. For example, if a red-flowered plant (RR) is crossed with a white-flowered plant (WW), the offspring (RW) might have pink flowers, showing an intermediate trait between red and white.
This phenomenon occurs because the dominant allele does not completely mask the effect of the recessive allele. Instead, both alleles contribute to the phenotype, leading to a mixed or intermediate expression. Incomplete inheritance is different from complete dominance, where the dominant allele completely masks the recessive allele, and codominance, where both alleles are fully expressed simultaneously.
Understanding incomplete inheritance helps in predicting the outcomes of genetic crosses and explains why some traits appear to blend in offspring rather than following the classic Mendelian ratios.