Select the correct statement regarding these genetic phenomenon

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. avery, mcleod and mc carty united the knowledge of chromosomal segregation with Mendelian principles and called it the chromosomal theory of inheritance.

Answer

To solve the question regarding the correct statement about genetic phenomena, we will analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Understanding Morgan's Dihybrid Crosses**:
- T.H. Morgan conducted dihybrid crosses in Drosophila melanogaster (fruit flies) to study inheritance patterns.
- He was instrumental in identifying sex-linked traits through these experiments.
- **Conclusion**: The first statement is correct.

2. **Recombination Frequency and Gene Mapping**:
- The second statement discusses the use of recombination frequency to determine the distance between genes on the same chromosome.
- It is true that a higher recombination frequency indicates that genes are further apart and less linked.
- This concept is fundamental in genetic mapping.
- **Conclusion**: The second statement is also correct.

3. **Phenylketonuria (PKU) and Its Inheritance**:
- The third statement addresses phenylketonuria, which is indeed an autosomal recessive disorder.
- PKU results from a deficiency in the enzyme phenylalanine hydroxylase, leading to the accumulation of phenylalanine and its derivatives, causing mental retardation.
- **Conclusion**: The third statement is correct.

4. **Chromosomal Theory of Inheritance**:
- The fourth statement claims that Avery, MacLeod, and McCarty united chromosomal segregation knowledge with Mendelian principles.
- However, the chromosomal theory of inheritance was actually proposed by Sutton and Boveri in 1902.
- Avery, MacLeod, and McCarty are known for their work on DNA as the genetic material, not for the chromosomal theory.
- **Conclusion**: The fourth statement is incorrect.

### Final Answer:
The correct statements regarding the genetic phenomena are the first three statements. The fourth statement is incorrect.