Question

Which of the following is the genotypic ratio of monohybrid cross?
A.1:2:1
B.9:7
C.1:2
D.9:3:3:1

Answer 1

Hint: Mendel conducted artificial pollination or cross-pollination experiments using several true-breeding pea lines. A true breeding line is one that having undergone continuous self-pollination, shows the stable trait inheritance and expression for several generations.

Complete answer:
Mendel selected a total of 14 true-breeding pea plant varieties, such as the height of the stem whether tall or dwarf as pairs which were similar except for one character with contrasting traits. It means, Mendel selected 7 characters that are seed shape, seed colour, pod colour in pea plant for carrying out hybridization experiments and to study inheritance
When heterozygous yellow seed is crossed with green seeded plants it is an example of monohybrid cross.
Study of inheritance of a single pair of contrasting traits of a character at a time is called one gene inheritance. Mendel crossed true breeding yellow seeds and true breeding green seeds variety of pea plants to study the inheritance of one gene.

The plants used in the initial cross are referred to as $\mathop P\nolimits_1 $, and $\mathop P\nolimits_2 $ or parents. Since pea is self-fertilising, the anthers should be removed from the female parent before maturity for the purpose of cross pollination.
The method of removal of anthers from bisexual flowers of female parent plant is called emasculation. The pollens, then at the dehiscence stage, are brought from the male parent and are dusted on the stigma of emasculated flowers.

He collected the seeds produced as a result of this cross and grew them to generate plants of the first hybrid generation. This generation is also called the filial, (offspring) progeny or the $\mathop F\nolimits_1 $.
When Mendel self-pollinated the yellow seeded $\mathop F\nolimits_1 $, plants, both yellow and green seeded plants were obtained in $\mathop F\nolimits_2 $, generation. Offspring derived from selfing of the $\mathop F\nolimits_1 $, are termed as second filial or $\mathop F\nolimits_2 $, generation. The proportion of plants that were yellow $\dfrac{3}{4}$ of the $\mathop F\nolimits_2 $, population while $\dfrac{1}{4}$ of the $\mathop F\nolimits_2 $, population were green. We must note here that green seeds which disappeared in $\mathop F\nolimits_1 $, generation, reappeared in $\mathop F\nolimits_2 $.

Hence, the correct answer is option (A)

Note: Mendel crossed pea plants differing in two characters (dihybrid cross) to verify the results of monohybrid crosses. This gave him a chance to understand inheritance of two pairs of factors like seed colour and shape at a time. A cross was made that is they are allowed for pollination between a pure round yellow-seeded pea plant (RRYY) with wrinkled green-seeded pea plant (rryy). Yellow colour is dominant over green and round seed shape over wrinkled seed shape.