Medical Oncologist
CION Cancer Clinics
Can a cancer gene really skip a generation? | CION Cancer Clinics
The gene itself does not skip a generation. A parent can carry a faulty gene, never develop cancer, and pass it to a child who does. From the outside that looks like a generation was missed. This page explains what actually produces that appearance, and how a counsellor checks a family tree that seems to have a gap. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- Can a cancer gene really skip a generation?
- What actually produces the appearance of a skipped generation
- How a counsellor works out whether a generation truly skipped
- Words this topic uses, in plain language
- What looks like skipping, and what is actually happening
- What families assume about a generation that looks skipped
- What this page cannot tell you
- Common questions about a gene that seems to skip a generation
The short answer
Can a cancer gene really skip a generation?
The gene itself does not skip. What can appear to skip is the illness. A parent can carry a faulty gene their entire life, never develop cancer, and pass the fault to a child who does. From the outside that looks like the fault vanished for a generation and reappeared. It was there the whole time.
Why this confuses families so often
Family trees are usually drawn from memory of who was ill, not from who was tested. If a grandparent was never diagnosed, most families assume they carried nothing at all, when in fact they may simply have been a carrier who never developed cancer.
Why it matters for how you read your own family tree
A gap in diagnoses does not rule out an inherited fault passing straight through that gap. This is one of the most common reasons a genetic counsellor asks about grandparents and even great-aunts and great-uncles, not just parents and siblings.
A gap in diagnoses is not the same as a gap in the fault. The two can look identical on paper.Four reasons it looks like skipping
What actually produces the appearance of a skipped generation
Each of these is a genuine, separate reason, and more than one can be true in the same family.
Incomplete penetrance
Not every carrier develops cancer. A parent can carry the fault and live a full, healthy life, then pass it to a child who is affected.
Never diagnosed, not never carried
Some relatives died of other causes before any cancer related to the fault could appear, or were never tested, so the record looks clean when it may not have been.
Small families hide patterns
A family with only one or two children per generation has fewer chances for a carrier to show up as affected, purely by how few people are in the tree.
Records that simply were not kept
Older generations, especially in India, often have thin medical records. An illness attributed to old age or never formally diagnosed can hide a cancer that was actually there.
Not sure whether this applies to you?
Ask an oncologistChecking a suspected gap
How a counsellor works out whether a generation truly skipped
Widen the family tree
Grandparents, great-aunts, great-uncles and their children are all asked about, not just the immediate family, to see whether the fault appears further along a branch.
Ask what each relative actually died of
"Old age" or "a stomach problem" sometimes means an undiagnosed cancer, especially for relatives who died decades ago without modern tests.
Test the person already affected first
If someone alive has cancer, testing them directly settles whether a fault exists, without needing to solve the historical puzzle at all.
Use the result to test upward, not just downward
If a fault is confirmed, testing a parent can show which side of the family it travelled through, even if that parent was never ill.
On your report
Words this topic uses, in plain language
- Penetrance
- How often a fault actually leads to cancer among everyone who carries it. It is never all of them, which is why some carriers stay well.
- Carrier
- Someone with the fault who has not developed cancer. A carrier can still pass the fault to a child.
- Obligate carrier
- Someone who, based on the family tree, must carry the fault even though they have never been tested or affected themselves.
- Pedigree
- The formal family tree a counsellor draws, marking who was affected, at what age, and how everyone is related.
- Germline
- Present in every cell from birth, which is what allows a fault to pass silently through an unaffected carrier to the next generation.
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Side by side
What looks like skipping, and what is actually happening
What it looks like
What is actually happening
Grandparent had no cancer, so nothing was passed on
Grandparent may be an unaffected carrier
The fault vanished for one generation
The fault was present the whole time, just silent
Only the grandchild is really at risk
Aunts, uncles and cousins on that branch may carry it too
The pattern is too irregular to mean anything
Incomplete penetrance produces exactly this kind of irregularity
Commonly believed
What families assume about a generation that looks skipped
"My grandmother never had cancer, so it can't have come from her side."
She may have carried the fault without ever developing cancer herself. An unaffected carrier passes the fault on exactly as an affected one would.
"If it skipped my father, it can't reach me."
A parent who is unaffected can still carry and pass on the fault. Being unaffected is not the same as not carrying it.
"There's no point testing someone who was never ill."
Testing an unaffected relative can still confirm whether they carry the fault, which tells you exactly which branch of the family it travelled through.
"A skipped generation means the risk is weaker now."
The fault itself does not weaken by passing through an unaffected carrier. A grandchild who inherits it carries the same raised risk as if their grandparent had been affected.
Being straight with you
What this page cannot tell you
It cannot tell you whether your own family's gap is a true skip or an unaffected carrier. That takes a properly drawn family tree and, in most cases, a genetic test on the relative who is already affected.
It cannot reconstruct records that were never kept
For relatives who died decades ago without a clear diagnosis, some uncertainty may never be resolved, especially where death certificates were never issued or have since been lost. A counsellor works with what is known and is honest with you about what is not.
Who this does not apply to
If nobody in your family has ever had an unusual pattern of cancer, a gap in diagnoses is probably just that: a gap, with no fault hiding inside it. This page is for families where a fault has already been confirmed somewhere in the tree, or where the pattern of diagnoses genuinely looks unusual.
If a relative's cause of death is unclear and you suspect it may matter, call the helpline. A counsellor can advise whether it is worth pursuing.Questions we are asked
Common questions about a gene that seems to skip a generation
Can a gene fault really disappear and come back?
No. What appears to disappear is the illness, not the fault itself. An unaffected parent can carry the fault their whole life and pass it to a child who does develop cancer.
Should we test relatives who were never ill?
Often yes, once a fault has been confirmed somewhere in the family. Testing an unaffected relative shows whether they are a carrier, which clarifies which branch of the family the fault runs through.
Why does my counsellor keep asking about grandparents?
Because a fault can pass silently through an unaffected grandparent. Widening the family tree beyond parents and siblings often reveals a pattern that a narrower tree would miss.
Does an unaffected carrier's child face lower risk?
No. The fault carries the same raised risk regardless of whether the parent who passed it on ever developed cancer themselves.
What if we don't know how a relative died?
Tell your counsellor what is known, even if it is vague. Sometimes old records or death certificates can be traced, and sometimes the gap simply remains unresolved.
Can incomplete penetrance run in some families more than others?
Penetrance can vary between different faults in the same gene and between families, which is one reason two families with the same gene named on their reports can look different on paper.
Is it worth testing a very elderly relative who has never had cancer?
It can be, since their result still tells you whether the fault runs through their side of the family. A counsellor can weigh whether it is worth arranging given their age and circumstances.
Who should we speak to about an unusual gap in our family history?
A genetic counsellor can look at the full family tree and tell you whether the gap is meaningful. Call the CION helpline if you are not sure how to reach one.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
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Sources
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- MedlinePlus Genetics — What are the different ways in which a genetic condition can be inherited?
- Cancer Research UK — Inherited cancer genes and increased cancer risk
- NHS — Predictive genetic tests for cancer risk genes
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
What penetrance meansWhy some carriers never develop cancerWhy the risk is 50% for each childThe maths behind how a fault passes to each childDoes it matter which parent it came from?Tracing a fault back through the family treeCancer genetics explainedThe basics, if you are starting from the beginning
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Does your family history have a gap you can't explain?
Tell us who was diagnosed, at what age, and where the gap sits. We will tell you honestly whether it is worth a genetic referral. One helpline serves every CION centre.