Final answer:
The 1:2:1 ratio of dwarf, medium, and tall offspring when medium-height hybrid plants are crossed is an example of incomplete dominance, where the heterozygote displays an intermediate phenotype.
Step-by-step explanation:
When certain medium-height hybrid plants were crossed, and they produced offspring that were dwarf, medium, and tall in a ratio of 1:2:1, this is an example of incomplete dominance. In incomplete dominance, neither allele is completely dominant over the other, resulting in a heterozygote phenotype that is intermediate between the two homozygote phenotypes. An example is the snapdragon (Antirrhinum magus), where crossing a red-flowered plant (CRCR) with a white-flowered plant (CWCW) produces pink-flowered offspring (CRCW), with a genotypic and phenotypic ratio of 1:2:1 for red: pink: white. This intermediate phenotype is distinctly different from Mendelian inheritance, where one allele is completely dominant over the other, and the resultant phenotypic ratio is 3:1 when both parents are heterozygous for the trait.