Select the correct statement.

Options

A. Morgan carried out several dihybrid crosses in Drosophila to study the genes that were sex linked.
B. Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and mapped their position on chromosome.
C. Phenylketonuria is an example of autosomal recessive inheritance.
D. Baveri united the knowledge of chromosomal segregation with Mendelian principles and called it the chromosomal theory of inheritance.

Answer

To solve the question, we need to evaluate each of the given statements and determine which one is correct.

### Step-by-Step Solution:

1. **Evaluate the First Statement**:
- The statement claims that Morgan carried out several dihybrid crosses in Drosophila to study sex-linked genes.
- However, it is known that Morgan primarily focused on monohybrid crosses to study sex-linked traits, particularly the white-eyed trait in Drosophila.
- **Conclusion**: This statement is incorrect.

2. **Evaluate the Second Statement**:
- The statement suggests that Stuart used the frequency of recombination between gene pairs on the same chromosome to measure the distance between genes and map their positions.
- While it is true that recombination frequency can be used to map genes, the statement does not accurately attribute this work to Stuart. This concept is more closely associated with geneticists like Morgan and Sturtevant.
- **Conclusion**: This statement is misleading and incorrect.

3. **Evaluate the Third Statement**:
- The statement claims that phenylketonuria (PKU) is an example of an autosomal recessive trait.
- In fact, PKU is indeed an autosomal recessive disorder caused by mutations in a single gene (the PAH gene). It is not a polygenic trait, as it is controlled by one gene.
- **Conclusion**: This statement is incorrect.

4. **Evaluate the Fourth Statement**:
- The statement indicates that Bavary united the knowledge of chromosomal segregation with Mendelian principles and called it the Chromosomal Theory of Inheritance.
- This is a true statement, as the Chromosomal Theory of Inheritance was indeed developed by scientists like Walter Sutton and Theodor Boveri, who integrated Mendelian genetics with the behavior of chromosomes during meiosis.
- **Conclusion**: This statement is correct.

### Final Answer:
The correct statement is the fourth one: "Bavary united the knowledge of chromosomal segregation with Mendelian principles and called it Chromosomal Theory of Inheritance."

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