Which of the following correctly organizes these genetic terms in order from smallest to largest?

The answer

Ordered from smallest to largest, the standard genetic hierarchy is:

nucleotide → gene → DNA molecule → chromosome

• A nucleotide is the basic unit of DNA — one sugar, one phosphate, and one nitrogenous base (A, T, G, or C).
• A gene is a specific sequence of nucleotides that codes for a product (usually a protein). It contains hundreds to thousands of nucleotides.
• A DNA molecule is a very long double strand of nucleotides that carries many genes strung along its length.
• A chromosome is that DNA molecule tightly wound around histone proteins and condensed into a compact structure. It is the largest item in the list.

Handling the common variations

Different quizzes swap in extra terms, which is where students get tripped up. Here is how the other common terms fit:

• base ≈ smaller than or part of a nucleotide (a base is one component of a nucleotide), so an order using "base" puts it first: base → nucleotide → gene → ...
• chromatin is the loose, uncondensed form of DNA+protein; it sits between DNA molecule and a fully condensed chromosome.
• nucleus and cell are larger than a chromosome, because a nucleus contains all the chromosomes and the cell contains the nucleus: ... chromosome → nucleus → cell.

A fuller size ladder therefore reads: base → nucleotide → gene → DNA molecule → chromosome → nucleus → cell. Whatever term set your question uses, drop the terms into this ladder and read off the order.

Why the reversed or scrambled options are wrong

• Putting chromosome first is the classic error — a chromosome is the most condensed, largest package, not the smallest unit.
• Putting gene before nucleotide is wrong because a gene is made of many nucleotides; the part cannot be larger than the whole it composes.
• Putting DNA molecule before gene is wrong because a single DNA molecule carries many genes; the molecule is the container, the gene is a segment within it.

The bigger picture

Think of it as nesting boxes. The smallest piece — a nucleotide — links with others to spell out a gene. Many genes lie along one long DNA molecule. That molecule coils up with proteins to form a chromosome. All the chromosomes together sit inside the nucleus, which sits inside the cell. Because each level is physically built from the smaller ones below it, the part-to-whole logic (part is always smaller than the whole it belongs to) reliably gives you the correct smallest-to-largest order for any version of this question.