Chromosome vs chromatid
Quick answer: A chromosome is a DNA package lineage; a chromatid is one copy of that package after replication.
Before S phase, an unreplicated chromosome is one DNA molecule package. After S phase, it has two sister chromatids until anaphase.
Use the table rows first for rapid contrast, then read the similarity and difference sections to lock in exam-ready language. Finish with the “when to use which term” guidance before attempting the self-checks.
Diagram
Side-by-side comparison
| Feature | Chromosome | Chromatid |
|---|---|---|
| Before S phase | One unreplicated chromosome | Term not used for sisters yet |
| After S phase | One duplicated chromosome | Two sister chromatids |
| Anaphase | Daughters become chromosomes | Sisters separate |
| Homologs | Maternal/paternal chromosomes | Not the same as sisters |
| Centromere | Present on chromosome | Sisters share cohesion at centromere |
| Student tip | X shape often means duplicated chromosome | Each arm of X is a chromatid |
Similarities
Both refer to packaged DNA units in cell division.
Both are essential mitosis vocabulary.
Differences
Chromatid implies a copy after replication.
Chromosome is the broader lineage term.
When each term applies
Use chromatid when counting copies before separation.
Use chromosome when discussing karyotype identity.
Common confusion
The classic mistake is calling each X a chromatid instead of a duplicated chromosome with two chromatids.
Common questions
How many chromatids does a duplicated chromosome have?
Two sisters.
What separates in mitotic anaphase?
Sister chromatids.
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