Question

Arrange the following steps of crossing over in correct order :
A. Pachytene stage
B. Synapsis of homologous chromosomes
C. Separation of homologous chromosomes
D. Breakage and reunion of chromatids
E. Formation of chiasmata
Choose the correct answer from the options given below :

• A. \(A, D, E, C, B\)
• B. \(D, B, C, A, E\)
• C. \(B, A, D, E, C\)
• D. \(A, D, C, B, E\)

Hint:

Remember: \[ \text{Synapsis} \rightarrow \text{Crossing Over} \rightarrow \text{Chiasmata} \]
• Zygotene \(\rightarrow\) Synapsis
• Pachytene \(\rightarrow\) Crossing over
• Diplotene \(\rightarrow\) Chiasmata visible

Answer 1

The Correct Option is C

Concept: Crossing over is the exchange of genetic material between homologous chromosomes during meiosis I. It occurs during prophase I and increases genetic variation. Important events associated with crossing over include:
• Synapsis of homologous chromosomes
• Formation of synaptonemal complex
• Exchange of chromatid segments
• Formation of chiasmata
• Separation of homologous chromosomes

Step 1: Synapsis of homologous chromosomes. The first event is: \[ \text{Pairing of homologous chromosomes} \] This process is called: \[ \text{Synapsis} \] Thus, the first step is: \[ \boxed{B} \]

Step 2: Pachytene stage. After synapsis, homologous chromosomes enter: \[ \text{Pachytene stage} \] During this stage:
• Chromosomes become fully paired.
• Crossing over begins. Thus, the next step is: \[ \boxed{A} \]

Step 3: Breakage and reunion of chromatids. Crossing over involves: \[ \text{Breakage and exchange of chromatid segments} \] followed by reunion of chromatids. Thus: \[ \boxed{D} \]

Step 4: Formation of chiasmata. After exchange of segments: \[ \text{Chiasmata become visible} \] Chiasmata represent points where crossing over has occurred. Thus: \[ \boxed{E} \]

Step 5: Separation of homologous chromosomes. Finally, homologous chromosomes separate during: \[ \text{Anaphase I} \] Thus: \[ \boxed{C} \] Therefore, the correct sequence is: \[ \boxed{B \rightarrow A \rightarrow D \rightarrow E \rightarrow C} \] Hence, the correct answer is: \[ \boxed{(C)\ B, A, D, E, C} \]