Question

When the tall plants with purple flowers were crossed with dwarf plants having white flowers, Mendel found the ratio of progeny to be
A. 1:2:1
B. 3:1
C. 9:3:3:1
D. 1:4:6:4:1

Answer 1

Dihybrid cross refers to a cross between two different genes of pure parents that differ in two pairs of observed traits or character. The character that is expressed in $F1$ progeny is known as dominant character and the character or the trait which is not expressed in $F2$ generation is referred as recessive character.

Complete answer:
The given question is entirely related to dihybrid cross in which the two pairs of factors are inherited independently. If the tall plant with purple flower TW is crossed with dwarf plant with white flowers tw, then in $F1$ progeny it will be TtWw. Then when this will be crossed again for $F2$ progeny, then the result of dihybrid cross Mendel gave the Law of Independent Assortment in which the phenotypic ratio will be 9:3:3:1.
Based on the probability, the four types of gametes of $F1$ dihybrids unite randomly in the process of fertilization and produce sixteen types of individuals in $F2$ in the ideal ratio of 9:3:3:1.

Hence, the correct answer is option (C).

Additional information:
Interactions which take place in between the alleles of the same gene (i.e., alleles at the same locus) in order to deviate from the mendelian inheritance patterns is known to be intragenic or intralocus or interallelic gene interaction.
The common examples for intragenic interaction include the following such as: 1) Incomplete dominance (2) Codominance (3) Multiple alleles (4) Pleiotropic genes.

Note: Gregor Johann Mendel who was the first systematic researcher in the field of genetics and was regarded as the father of Genetics. Through his experiments and studies on garden pea plants, he unraveled the mystery of heredity.