Hierarchical sizes of genetic material

Steps:

• Define gene as a specific sequence of nucleotides on DNA that codes for a protein or trait.
• Define DNA molecule as a long polymer chain of nucleotides containing many genes.
• Define chromosome as a condensed structure of one or more DNA molecules packaged with proteins.
• Order by size: gene (thousands of base pairs) < DNA molecule (millions of base pairs) < chromosome (entire genome portion).

Why A is correct:

• A gene is a subunit of a DNA molecule, which forms the core of a chromosome, establishing the size order from smallest to largest per molecular biology definitions.

Why the others are wrong:

• B: DNA molecule encompasses multiple genes, so it is larger than a gene.
• C: Chromosome is the largest structure, containing the entire DNA molecule.
• D: Chromosome contains the DNA molecule, making it larger, not smaller.

Final answer: A