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Medical glossary

Chromosome

A chromosome is a tightly packed form of DNA that carries genes. A human cell usually has 46 chromosomes (23 pairs).

Last updated: ~1 min read
Two dividing cells with their chromosomes visible under the microscope, next to other nuclei
Figure 1.Chromosomes become visible in a dividing cell

01Short answer

One chromosome of each pair comes from the mother and one from the father; the 23rd pair determines sex (XX or XY). In leukaemia, chromosomes can break, swap pieces (translocation), be lost or be duplicated. These changes are seen with karyotype and FISH and help define the risk group. For example, t(9;22) creates the Philadelphia chromosome.

02Simple explanation

Packed DNA.

46 chromosomes.

Changes are possible.

Seen in a karyotype.

03Scientific explanation

NCI: a chromosome is a structure in the cell nucleus that carries genes.

The NCI Dictionary explains cancer terms in plain language; check the exact meaning for your situation with your doctor.

04What happens in the body?

Shorthand

t means translocation, del means deletion, + means extra.

Packing
Figure 2.Packing — Chromosome

Why it matters

Outlook and treatment choice.

Shown: 23 pairs
Figure 3.Shown: 23 pairs — Chromosome

Where you will see this word

In test results, discharge letters and conversations with your doctor. Write the word down and ask what it means.

Ask your doctor

The general meaning and the meaning of your own result can differ. The most important question is “What does this mean for me?”

05From an unfamiliar word to a clear answer: four steps

Write it down, look it up, prepare a question, ask.

Write it down — From a result or a conversation.1Write it downFrom a result or a conversation.
Look it up — Learn the plain meaning.2Look it upLearn the plain meaning.
Prepare a question — What does this mean for me?3Prepare a questionWhat does this mean for me?
Ask — Your doctor gives the personal explanation.4AskYour doctor gives the personal explanation.
UnderstandingResults feel less frightening.
ConversationA shared language with your doctor.
SafetyNot drawing conclusions alone.

06Key points at a glance

TopicIn brief
Shorthandt means translocation, del means deletion, + means extra.
Why it mattersOutlook and treatment choice.
Where you will see this wordIn test results, discharge letters and conversations with your doctor. Write the word down and ask what it means.
Ask your doctorThe general meaning and the meaning of your own result can differ. The most important question is “What does this mean for me?”

07Key terms

Translocation
Two chromosomes exchanging pieces.
Trisomy
Three copies of one chromosome.
Term
A word with a precise medical meaning.
Reference range
The range a laboratory considers normal.

08Key points

  • Learn.
  • Ask your doctor.
  • Write it down.
  • Write the word down.
  • Ask what it means.

09Frequently asked questions

Are chromosome changes inherited?

In leukaemia, usually not.

What is “monosomy 7”?

Loss of one copy of chromosome 7; your doctor will explain what it means.

This word is in my results: should I worry?

The word itself does not mean a serious or mild condition; get the explanation from your doctor.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Are chromosome changes inherited?

  2. What is “monosomy 7”?

  3. This word is in my results: should I worry?

My questions

12Sources

  1. National Cancer Institute. NCI Dictionary of Cancer Terms: chromosome
  2. MedlinePlus Genetics. Help Me Understand Genetics: The basics
  3. National Cancer Institute. NCI Dictionary of Cancer Terms: cytogenetics
  4. National Cancer Institute. NCI Dictionary of Cancer Terms
  5. National Cancer Institute. Leukemia
  6. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: peripherally inserted central catheter
  7. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: stem cell transplant
  8. American Cancer Society. Low Blood Counts
  9. National Cancer Institute. NCI Dictionary of Cancer Terms: biopsy
  10. National Cancer Institute. NCI Dictionary of Cancer Terms: karyotyping
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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