It is said thet Mendel proposed that the factor controlling any character is discrete and independen. His proposition was based on the

Options

A. result of `F_(3)`-generation of a cross
B. observations that the offspring of a cross made between the plants having two contrasting characters shows only character without any blending
C. self-pollination of `F_(1)` offsprings
D. cross-pollination of `F_(1)`-generation with recessive parent

Explanation

### Step-by-Step Text Solution:

1. **Understanding Mendel's Proposition**: Mendel proposed that the factors controlling traits (now known as genes) are discrete units that do not blend together. This means that when two contrasting traits are crossed, the offspring will exhibit one trait or the other, not a mixture of both.

2. **Observation of F1 Generation**: When Mendel crossed plants with contrasting traits (e.g., tall vs. dwarf), the first generation (F1) of offspring displayed only one of the two traits. For example, if he crossed tall plants with dwarf plants, all F1 offspring were tall, demonstrating that the tall trait was dominant.

3. **F2 Generation and Ratios**: When Mendel allowed the F1 generation to self-pollinate, he observed the F2 generation. In this generation, the traits segregated in a specific ratio (3:1 for a monohybrid cross), confirming that the traits were discrete and independent.

4. **Contrasting Characters**: Mendel's experiments involved contrasting characters, such as round vs. wrinkled seeds or yellow vs. green seeds. He noted that these traits did not blend in the offspring, which supported his idea of discrete inheritance.

5. **Conclusion**: Mendel's conclusion was that the factors (alleles) controlling traits are inherited independently of one another, leading to the concept of independent assortment. This was based on his observations of the F2 generation, where traits segregated without blending.

### Final Answer:
Mendel's proposition that the factor controlling any character is discrete and independent was based on the observation that the offspring of a cross made between plants having two contrasting characters shows only one character without any blending (Option B).

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