1:2:1 phenotypic and genotypic ratios occur in case of
(a) Blending/intermdiate inheritance
(b) Pseudoalleles
(c) Multiple alleles
(d) Complementary genes

Options

A. Blending/intermdiate inheritance
B. Pseudoalleles
C. Multiple alleles
D. Complementary genes

Answer

To solve the question regarding which scenario produces a 1:2:1 phenotypic and genotypic ratio, we can analyze each option step by step.

### Step 1: Understand the Ratios
The 1:2:1 ratio indicates that there are three different phenotypes or genotypes resulting from a genetic cross. This ratio typically arises in certain inheritance patterns.

### Step 2: Analyze Each Option
- **(a) Blending/intermediate inheritance**: In this type of inheritance, the traits of both parents blend together in the offspring. For example, if one parent has a red flower and the other has a white flower, the offspring may have pink flowers. This results in a 1:2:1 ratio for both phenotypes and genotypes when considering a monohybrid cross.

- **(b) Pseudoalleles**: Pseudoalleles do not produce a consistent phenotypic or genotypic ratio. They can exhibit various patterns of inheritance depending on the alleles involved, thus they do not yield a 1:2:1 ratio.

- **(c) Multiple alleles**: Similar to pseudoalleles, multiple alleles can lead to a variety of genotypes and phenotypes, and the ratios depend on the specific alleles involved. Therefore, they do not consistently produce a 1:2:1 ratio.

- **(d) Complementary genes**: This type of genetic interaction typically results in a phenotypic ratio of 9:7, not 1:2:1. The genotypic ratio can also differ, thus this option is not correct.

### Step 3: Conclusion
After analyzing all the options, we find that only **(a) Blending/intermediate inheritance** results in a 1:2:1 phenotypic and genotypic ratio. Therefore, the correct answer is:

**Answer: (a) Blending/intermediate inheritance**