Polyploidy in crop evolution—Raphanobrassica Raphanobrassica (radish × cabbage amphidiploid) is a classical example of which chromosomal condition?

Introduction / Context:
Allopolyploids arise from hybridization between different species followed by chromosome doubling, restoring fertility. Raphanobrassica is a well-known experimental amphidiploid produced from radish (Raphanus) and cabbage (Brassica).

Given Data / Assumptions:

• Parents belong to different genera/species.
• Hybrid fertility is restored after chromosome doubling.
• Resulting organism carries complete chromosome sets from each parent.

Concept / Approach:
Allopolyploidy (amphidiploidy) involves combining two distinct but complete genomes. This is distinct from aneuploidy (loss/gain of one or few chromosomes) and nullisomy (loss of a homologous pair). Autopolyploidy duplicates the same genome, not different ones.

Step-by-Step Solution:

Verification / Alternative check:
Cytological pairing and fertility recovery after doubling confirms amphidiploid status in such hybrids.

Why Other Options Are Wrong:

• Aneuploidy/nullisomy: partial chromosome number changes, not whole-genome combinations.
• Autopolyploidy: duplicates the same genome rather than merging two species’ genomes.
• Haploidy: half the somatic chromosome number, typically sterile.

Common Pitfalls:
Confusing any polyploid with allopolyploid; always ask if the genomes are from different species.

Final Answer:
Allopolyploidy (amphidiploidy)