Incomplete Dominance MCQ - Practice Questions & Answers

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Incomplete Dominance

Mendel’s results, that traits are inherited as dominant and recessive pairs, contradicted the view at that time that offspring exhibited a blend of their parents’ traits.
When experiments on peas were repeated using other traits in other plants, it was found that sometimes the F1 had a phenotype that did not resemble either of the two parents and was in between the two.
For example, in the snapdragon, Antirrhinum majus a cross between a homozygous parent with white flowers (rr) and a homozygous parent with red flowers (RR) will produce offspring with pink flowers (Rr).
This pattern of inheritance is described as incomplete dominance, denoting the expression of two contrasting alleles such that the individual displays an intermediate phenotype.
Here the genotype ratios were exactly as we would expect in any mendelian monohybrid cross, but the phenotype ratios had changed from the 3:1 dominant : recessive ratio.
What happened was that R was not completely dominant over r and this made it possible to distinguish Rr as pink from RR (red) and rr (white).
The allele for red flowers is incompletely dominant over the allele for white flowers.
However, the results of a heterozygous self-cross can still be predicted, just as with Mendelian dominant and recessive crosses.
In this case, the genotypic ratio would be 1:2:1.