Question

Human chromosome 2, a large metacentric chromosome is the result of ___________ during the course of evolution. 
 

• A. Translocation
• B. Robertsonian translocation
• C. Chromosomal replication
• D. Chromosomal elongation

Hint:

Remember the key evidence: Humans have 46 chromosomes, chimps have 48. The fusion of two ape chromosomes created our chromosome 2. This specific type of fusion of two chromosomes at the centromere is called a Robertsonian translocation.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The question asks about the specific chromosomal event in human evolution that led to the formation of chromosome 2. Humans have 23 pairs of chromosomes, while other great apes (like chimpanzees) have 24 pairs. This difference is explained by a fusion event.
Step 2: Detailed Explanation:
- Cytogenetic evidence shows that human chromosome 2 corresponds to two separate smaller chromosomes in other great apes.
- It is hypothesized that in the human lineage, two ancestral acrocentric (where the centromere is near one end) chromosomes fused end-to-end to form the large, metacentric (centromere in the middle) chromosome 2 that we see today.
- This specific type of chromosomal rearrangement, where two acrocentric chromosomes fuse at or near their centromeres, is called a Robertsonian translocation. Evidence for this includes the presence of a defunct, relic centromere and telomere sequences (normally found at the ends of chromosomes) in the middle of human chromosome 2.
- "Translocation" is a general term, while "Robertsonian translocation" is the precise term for this event. "Chromosomal replication" and "elongation" are incorrect processes.
Step 3: Final Answer:
The formation of human chromosome 2 is a classic example of a Robertsonian translocation event in evolution.