Chloroplast genetics What is the approximate size of the tobacco (Nicotiana tabacum) chloroplast genome?

Introduction / Context:
Chloroplast genomes are circular DNAs encoding photosynthetic and gene expression functions. Tobacco is a classic model for plastid transformation and genome mapping.

Given Data / Assumptions:

• Chloroplast genomes in higher plants are typically in the 120–170 kb range.
• Tobacco plastome is one of the best-characterized reference plastomes.

Concept / Approach:
Recall the canonical tobacco plastid genome size used in transformation vectors and maps. The commonly cited size is about 155 kb, featuring large and small single-copy regions separated by inverted repeats.

Step-by-Step Solution:

Verification / Alternative check:
Plastome maps used in biolistic transformation and marker insertion are based on ~155 kb tobacco chloroplast DNA.

Why Other Options Are Wrong:

• 55 kb and 15 kb: far below known plastome sizes.
• 325 kb and 375 kb: exceed higher-plant plastome sizes.

Common Pitfalls:
Confusing bacterial genome sizes or mitochondrial genome variability with the relatively conserved plastid genome range.

Final Answer:
155 kilobase