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Incomplete Dominance MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET

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F2 generation in a Mendelian cross showed that both genotypic and phenotypic ratios are same as 1: 2: 1. It represents a case of:

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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.

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Incomplete Dominance

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Incomplete Dominance

Biology Textbook for Class XII

Page No. : 76

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