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

Options

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

Answer

To determine the reason for the genetic ratio of 9:3:3:1, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Genetic Ratio**: The genetic ratio of 9:3:3:1 typically arises from a dihybrid cross, which involves two traits that are being studied simultaneously.

2. **Identifying the Dihybrid Cross**: A dihybrid cross involves organisms that are heterozygous for two traits. For example, if we consider two traits such as seed color (yellow vs. green) and seed shape (round vs. wrinkled), we can represent these traits with the following alleles:
- Yellow (Y) is dominant over green (y)
- Round (R) is dominant over wrinkled (r)

3. **Gamete Formation**: In a dihybrid cross, the alleles segregate independently during gamete formation. This means that the alleles for one trait do not influence the segregation of alleles for another trait. For example, the gametes produced by a YyRr individual would be YR, Yr, yR, and yr.

4. **Punnett Square Analysis**: By setting up a Punnett square for the cross between two YyRr individuals, we can predict the offspring's genotypes. The resulting combinations will yield:
- 9 Yellow Round (YYRR, YYRr, YyRR, YyRr)
- 3 Yellow Wrinkled (YYrr, Yyrr)
- 3 Green Round (yyRR, yyRr)
- 1 Green Wrinkled (yyrr)

5. **Conclusion**: The ratio of 9:3:3:1 is a result of the independent assortment of genes, as proposed by Gregor Mendel in his law of independent assortment. This law states that alleles for different traits segregate independently of one another during gamete formation.

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

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