A Monohybrid cross is the hybrid of two individuals with homozygous genotypes which results in the opposite phenotype for a certain genetic trait.
When red (RR) and white (rr) snapdragon flowers were crossed, the F1 generation flowers were all pink (Rr) in colour. When the F1 parents where self crossed, the F2 progeny showed new trait of pink coloured flowers along with parental traits namely red and white. This is due to blending of both the dominant and recessive traits, wherein intermediate colours were observed, that is pink in both F1 and F2 generations. This is called incomplete dominance.
Now, let’s see the possible genetic combinations in the Punnett square, by combining the parent alleles
F1 generation: all flowers are pink (Rr)
F2 generation: in this, phenotypic ratio is 1(red):2 (pink):1 (white)
genotypic ratio is 1(RR):2(Rr):1(rr)
hence, the phenotypic and genotypic ratios are same.
But, if you compare the same with Mendels trait of pea flowers with purple and white colour, it is as shown below:
F1 generation: all flowers are purple(Pp)
F2 generation: here, phenotypic ratio is 3(purple):1(white) genotypic ratio is 1((PP):2(Pp):1(pp)
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