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Incomplete dominance
Appears in
Concepts tested here
- Incomplete dominance ratio
- Snapdragon flower colour
All Questions
2012 AIPMT-PRE 1 question
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$F_2$ generation in a Mendelian cross showed that both genotypic and phenotypic ratios are same as 1 : 2 : 1. It represents a case ofIn incomplete dominance the heterozygote has an intermediate phenotype, so each genotype has its own phenotype.
In Mirabilis jalapa or snapdragon the $F_2$ shows 1 red (RR) : 2 pink (Rr) : 1 white (rr), so the phenotypic and genotypic ratios are both 1 : 2 : 1.
With complete dominance the phenotypic ratio would be 3 : 1.
2010 AIPMT-MAINS 1 question
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In $Antirrhinum$ two plants with pink flowers were hybridized. The $F_1$ plants produced red, pink and white flowers in the proportion of 1 red, 2 pink and 1 white. What could be the genotype of the two plants used for hybridization? Red flower colour is determined by RR, and white by rr genes.In $Antirrhinum$ (snapdragon) flower colour shows incomplete dominance: RR is red, rr is white and the heterozygote Rr is pink, because R is not completely dominant over r.
Both parent plants are pink, so each must be Rr.
Cross: $Rr \times Rr$; gametes from each parent: R and r.
Offspring: 1 RR : 2 Rr : 1 rr
Phenotypes: 1 red : 2 pink : 1 white, exactly as observed (phenotypic ratio = genotypic ratio).
Hence the genotype of both plants is Rr.