Question

Which of the following plant species has largest genome?

• A. Barley
• B. Zea mays
• C. Bread wheat
• D. Rice

Hint:

Genome size hierarchy: Rice $<$ Maize $<$ Barley $<$ Wheat.
Wheat is the "Giant" of plant genomes because it is a "Hybrid of Hybrids" (Hexaploid).
Paris japonica holds the record for the largest known plant genome overall (~150 Gb)!

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to compare the total amount of DNA (genome size) across four major cereal crops. Genome size is usually measured in Gigabase pairs (Gb) or picograms (C-value).

Step 2: Detailed Explanation:

• Rice (Oryza sativa): Has a very small, compact genome of approximately 0.4 Gb. This is why it was the first cereal to be fully sequenced.

• Maize (Zea mays): Has a moderate genome size of about 2.3 Gb, largely due to a high percentage of repetitive transposable elements.

• Barley (Hordeum vulgare): Has a large genome of about 5.1 Gb.

• Bread Wheat (Triticum aestivum): This is an allohexaploid species ($2n=6x=42$). It contains three distinct sub-genomes (AABBDD) inherited from different ancestral grass species. Because of this polyploidy, its genome is massive, approximately 16 to 17 Gb.

• Comparison: The wheat genome is roughly 40 times larger than rice and about 6-7 times larger than maize. Its sheer size and repetitive nature made its sequencing one of the greatest challenges in plant genomics.

Step 3: Final Answer:
Due to its hexaploid nature, Bread wheat possesses the largest genome among the options provided.