Question

The percentage of true-breeding plants in the ${F_2}$ generation of a monohybrid cross is _____.
A. 10
B. 30
C. 50
D. 70

Answer 1

Monohybrid cross is also known as one gene interaction. As the name suggests, it refers to the cross between two organisms in which only one contrasting character is considered. Moreover, ${F_2}$ generation refers to the filial 2 generation or the second generation.

Complete answer: Monohybrid cross is the cross in which only one set of contrasting characters is studied. When two true-breeding plants are taken and crossed together, then the first generation possesses all similar kinds of plants. This is because true-breeding plants will be homozygous. And since we are taking contrasting characters, one will be the dominant homozygous form of the allele whereas, another will be the recessive homozygous form of the same allele. By crossing these two plants, the offspring will be obtained with the same genotype. All the offerings will be Heterozygous and will possess the same set of characteristics. This means that all will be hybrid and none will be true or purebred. Now to obtain the second generation, we will take two plants from the first generation and cross them. since the parents will be heterozygous now, segregation of alleles will occur. Each allele will segregate independently and then combine with other alleles to form the gametes. Due to this reason, the original plants will be expressed in the second-generation progeny. Twenty-five percent of plants produced will be dominant homozygous and twenty-five percent plants produced will be recessive homozygous. Moreover, fifty percent of the plants will be recombinants or hybrids. Therefore, all the possible genotypes will be shown in the second generation. Thus, based on the above information we can conclude that the percentage of true-breeding plants in the ${F_2}$ generation of a monohybrid cross is 50.
Hence, the correct answer is option (C).

Note: The phenotypic ratio of the second generation of the monohybrid cross is $3:1$. This is because phenotype refers to the externally observable characters. And in the second generation, seventy-five percent of plants show the character of the dominant trait while only twenty-five percent of plants show the character of the recessive trait. On the other hand, the genotypic ratio of the second generation of the monohybrid cross is $1:2:1$. This is because the genotype refers to the genetic constitution of any character. And in the second generation of the monohybrid cross twenty-five percent of plants produced are dominant homozygous, fifty percent of the plants produced are recombinants or the hybrids, and twenty-five percent plants produced are recessive homozygous.