Question

A snapdragon plant homezygous for red flower when crossed with a white flowered plant of the same species produced pink flowers in `F_(1)` generation.
(a) What is the phenotypic expression called ?
(b) Work out the cross to show the `F_(2)` generation when `F_(1)` was self-pollinated. Give the phenotypic and genotypic ratios of `f_(2)` generation.
(c) How do you compare the `f_(2)` phenotypic and genotypic ratios with those of Mendelian monohybrid `f_(2)` ?

Answer 1

In Snapdragon plant (dog flower)

This phenotypic expression is called incomplete dominance, that is R is not fully dominant over r. We can say that F has a phenotype that did not resemble either of the two parents and it is intermediate in expression
(b) When `F_1` is self pollinated, the `F_2` is obtained.

`F_1` Phenotypic Ratio: 1 red: 2 Pink: 1 White
`F_2` Genotypic Ratio: 1 RR: 2 Rr: 1 r When F was self pollinated. the `F_2` is obtained. Due to incomplete dominance phenotypic ratio as well as genotypic ratios are same Le. 1:2:1 (c ) The Mendelian monohybrid ratio is `F_2` Phenotypic Ratio 3:1
`F_2` Genotypic Ratio 1: 2:1.
Both are different. But in incomplete dominance, they are same i.e. 1:2:1
The Mendelian monohybrid ratio defines complete dominance where one trait is dominant over the other trait called the recessive that is hidden in `F_1` but reappears in `F_2` generation.