48. Triticumaestivum is an example of
(1) Allopolyploid
(2) Autopolyploid
(3) Chromosome doubling
(4) Auto-allopolyploid

Core explanation

• Common bread wheat, Triticum aestivum, has genome composition AABBDD with 2n = 42.

• These three distinct chromosome sets (A, B, and D genomes) came from different ancestral species via two sequential interspecific hybridization events followed by chromosome doubling.​

• Possessing complete, diverged genomes from different species is the defining feature of an allopolyploid.​

So, Triticum aestivum is a textbook example of an allopolyploid.

Option-wise explanation

1. Allopolyploid – correct

   • Arises from hybridization between different species plus chromosome doubling.

   • Bread wheat combines genomes from multiple ancestral grass species (A, B, D), fitting this definition precisely.​

2. Autopolyploid

   • Formed by duplication of the genome within a single species (e.g., AAAA).

   • All chromosome sets come from the same species; not true for T. aestivum.

3. Chromosome doubling

   • Chromosome doubling is a mechanism that occurs in both auto- and allopolyploids.

   • It describes the process, not the category; the question asks for the “example of” what type of polyploid.

4. Auto-allopolyploid

   • A mixed or less standard term suggesting both auto- and allopolyploid features; not how bread wheat is classically defined.

   • Standard cytogenetics and textbooks consistently describe Triticum aestivum as an allohexaploid allopolyploid.

Therefore, Triticum aestivum is best classified as an allopolyploid (option 1).