Question

A pea plant with blue color flower BB is a crossbreed with a pea plant with a white flower denoted by ww. What will be the percentage of plants bearing white flowers in the ${ F }_{ 2 }$ generation, when the flowers of ${ F }_{ 1 }$ plants were selfed?

Answer 1

The ${ F }_{ 1 }$ generation is self-pollinated, therefore there's no change in traits in this generation. The${ F }_{ 2 }$ is carried out by cross-pollination with the white flowers so both colored flowers will appear in this generation.

Complete answer:
If the flowers of ${ F }_{ 1 }$ plants were selfed, the diagram below will represent the ${ F }_{ 2 }$ generation:

Therefore, from the diagram we get,
The F2 generation will be of 3 blue and 1 white flower. Therefore, the ratio will be a blue flower: white flower = 3:1.
Now,
The percentage of white flowers in the F2 generation is
Percentage $=\frac { No. \ of \ white \ flower \ plants }{ Total \ plants \ in \ { F }_{ 2 } \ generation } \times \ 100$
Percentage $=\frac { 1 }{ 4 } \times 100$
So, the percentage will be $25\%$.

Note:
- When purebred organisms of two different species are bred to give rise to a new type of animal or plant it is known as crossbreeding. It is used to create higher quality animals or plants with vitality and good health, sometimes irresponsible crossbreeding may cause deterioration of quality as well. In animal breeding, when the breeding is between single species it is called crossbreeds whereas in different species it is known as hybrids. But in the case of plants, these two terms are not distinguishable.
- When the stamen of a flower lands on the same flower's stigma during pollination it is called selfed or self-pollination. The term selfed is not restricted to self-pollination though, it can be referred to as self-fertilization as well. Self-pollination can be helpful in some cases such as keeping certain traits in the progenies stable. When there's no pollinating agent, the plants still need to carry out reproduction. In such a case, self-pollination can be a way to solve this problem. Also, there's less wastage of pollen during this process.