The ratio of 9:3:3:1 is due to

Options

A. Segregation of characters
B. Independent assortment of genes
C. Crossing over of chromosomes
D. Homologous pairing between chromosomes.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the genetic ratio of 9:3:3:1, which is commonly observed in the offspring of a specific type of genetic cross.

2. **Identifying the Type of Cross**: The ratio of 9:3:3:1 is characteristic of a dihybrid cross, which involves two pairs of contrasting traits. In this case, we are looking at traits such as seed color (yellow vs. green) and seed shape (round vs. wrinkled).

3. **Setting Up the Dihybrid Cross**: In a typical dihybrid cross, one parent is homozygous for both dominant traits (e.g., yellow round seeds) and the other parent is homozygous for both recessive traits (e.g., green wrinkled seeds).

4. **F1 Generation**: When these two parents are crossed, all offspring in the F1 generation will be heterozygous for both traits (e.g., YyRr), exhibiting the dominant traits (yellow and round).

5. **F2 Generation**: When the F1 generation is self-pollinated, the F2 generation is produced. The phenotypic ratio of the offspring in this generation can be determined using a Punnett square or by applying Mendel's laws.

6. **Calculating the Ratio**: The resulting phenotypic ratio from the F2 generation will be:
- 9 Yellow Round (dominant for both traits)
- 3 Yellow Wrinkled (dominant for color, recessive for shape)
- 3 Green Round (recessive for color, dominant for shape)
- 1 Green Wrinkled (recessive for both traits)

7. **Conclusion**: This 9:3:3:1 ratio is a result of the independent assortment of genes, which states that the alleles for different traits segregate independently of one another during gamete formation.

**Final Answer**: The ratio of 9:3:3:1 is due to the independent assortment of genes.

---