Mendelian Disorders

To solve the problem, we need to determine the number of pairs of contrasting characters in pea plants that were selected by Gregor Mendel for his experiments.

1. Understanding Mendel's Experiments:
Gregor Mendel, often referred to as the "Father of Genetics," conducted a series of experiments on pea plants (Pisum sativum) at the Abbey of St. Thomas in Brno, Moravia (now part of the Czech Republic). His work laid the foundation for modern genetics.

2. Contrasting Characters Studied by Mendel:
Mendel carefully selected seven distinct traits (or characteristics) of pea plants and observed how these traits were passed from one generation to the next. These traits included:

• Seed shape: Round vs. wrinkled
• Seed color: Yellow vs. green
• Pod shape: Inflated vs. constricted
• Pod color: Green vs. yellow
• Flower position: Axial vs. terminal
• Flower color: Purple vs. white
• Plant height: Tall vs. dwarf

3. Counting the Pairs:
Each of these traits represents a pair of contrasting characters. For example, "round vs. wrinkled" is one pair, "yellow vs. green" is another, and so on. Since Mendel studied seven such traits, there are seven pairs of contrasting characters.

4. Final Answer:
The correct answer is therefore .

To solve the problem, we need to determine the phenotype ratio observed in the F2 generation of a dihybrid cross. A dihybrid cross involves two different traits, each controlled by two alleles (one dominant and one recessive). The classic example is Mendel's experiment with pea plants, where he crossed plants differing in two traits (e.g., seed shape and seed color).

1. Understanding Dihybrid Cross:
In a dihybrid cross, the F1 generation is heterozygous for both traits (e.g., ), where and are dominant alleles, and and are recessive alleles. When the F1 generation self-fertilizes, the F2 generation results from the combination of all possible gametes.

2. Punnett Square Analysis:
The F1 generation produces four types of gametes: , , , and . When these gametes combine during fertilization, they produce 16 possible combinations in the F2 generation. These combinations can be organized into a 4x4 Punnett square.

3. Phenotype Ratios:
In the F2 generation, the phenotypes are determined by the expression of dominant and recessive alleles. For two traits, the expected phenotype ratio is derived as follows:

• 9 individuals will have both dominant phenotypes (e.g., round and yellow seeds).
• 3 individuals will have one dominant and one recessive phenotype (e.g., round and green seeds).
• 3 individuals will have the other dominant and recessive phenotype (e.g., wrinkled and yellow seeds).
• 1 individual will have both recessive phenotypes (e.g., wrinkled and green seeds).

This results in a phenotype ratio of .

4. Conclusion:
The correct answer is the phenotype ratio observed in the F2 generation of a dihybrid cross, which is .

Final Answer: