The following statements were noted by a student of grade 12 after studying about Morgan's dihybrid cross experiments with Drosophila.
1. Two genes chosen in a dihybrid cross are always located on the same chromosome.
2. Genes on the same chromosome are often linked.
3. Linked genes segregate independently during gamete formation.
4. Linked genes do not always obey the law of independent assortment.
Which of these statement(s) is/are TRUE?

Options

A. only 1
B. only 1 and 2
C. only 2 and 4
D. all- 1, 2, 3 and 4

Answer

To determine which statements about Morgan's dihybrid cross experiments with Drosophila are true, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: Two genes chosen in a dihybrid cross are always located on the same chromosome.**
- This statement is **FALSE**. In a dihybrid cross, the two genes can be located on the same chromosome or on different chromosomes. The key aspect of a dihybrid cross is that it examines the inheritance of two traits, which may or may not be linked.

2. **Statement 2: Genes on the same chromosome are often linked.**
- This statement is **TRUE**. Genes that are located on the same chromosome tend to be inherited together due to their proximity, which is referred to as genetic linkage. However, this does not mean they are always linked, as crossing over can separate them during meiosis.

3. **Statement 3: Linked genes segregate independently during gamete formation.**
- This statement is **FALSE**. Linked genes do not segregate independently; instead, they tend to be inherited together unless crossing over occurs. The law of independent assortment applies to genes located on different chromosomes.

4. **Statement 4: Linked genes do not always obey the law of independent assortment.**
- This statement is **TRUE**. Linked genes typically do not follow the law of independent assortment because they are located on the same chromosome and are often inherited together. This is a fundamental concept in genetics that explains why linked genes can show different inheritance patterns compared to unlinked genes.

### Summary of True Statements:
- The **TRUE** statements are:
- Statement 2: Genes on the same chromosome are often linked.
- Statement 4: Linked genes do not always obey the law of independent assortment.