Question

When a snapdragon plant bearing pink flowers was selfed, it was found that 69 plants were having red-colored flowers. What would be the number of plants bearing pink flowers and white flowers? Show with the help of Punnett square. Identify the principle of inheritance involved in this experiment.

Answer 1

Hint Mendel developed a method through which he was able to determine the progeny being produced would have either parental character or the recombinant character. He used a monohybrid and dihybrid cross in which one character and two characters were tested respectively. His cross was based on the external features that were visible in the pea plants.

Complete answer:
The snapdragon flower has three types of flowers that grow on them. The dominant type of flower is the red flower and the recessive type of flower is the white-colored flower. When these two flowers were crossed a new flower color of the flower emerged which was the pink flower. The pink flower is the heterozygous flower. This showed the incomplete inheritance of the character in the flower. If the red color flower is denoted by RR and the white color flower by rr then the pink flowers will be denoted by Rr. When the pink flowers are selfed-

| R| r
---|---|---
R| RR| Rr
r| Rr| rr

So, the progeny obtained had a single RR and rr offspring and two Rr offspring were obtained.
The ratio can be written as 1:2:1
If the RR offspring obtained were 69 then rr offspring’s will also be 69 and Rr offspring would be 138.
RR = 69
rr = 69
Rr = $2\times 69$=138
In this experiment, the incomplete dominance principle of inheritance can be seen. In incomplete dominance, the dominant character is not able to show itself completely in the heterozygous offspring which leads to the formation of a hybrid variety of offspring which has both mixed character of dominant as well as the recessive parent. This case can be clearly seen in snapdragon plant flowers.

Note: The Snapdragon flower shows incomplete dominance in them. In the heterozygous flowers, they are unable to show the red color (dominant) and neither white color (recessive) is able to express itself fully. In such a condition a pink flower is born which shows only some part of both the color.