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CION Cancer Clinics
Does it matter which parent a gene fault came from? | CION Cancer Clinics
For most inherited cancer genes, it does not matter whether the fault came from your mother or your father; it carries the same raised risk either way. What usually differs is which side of the family gets asked about closely. This page explains why the father's side is so often left out, and how a fault is traced back properly. 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
- Does it matter which parent a gene fault came from?
- If the gene behaves the same, what changes by side?
- How a counsellor decides which side to look at
- Words this topic uses, in plain language
- Autosomal genes versus the rare sex-linked exceptions
- What families get wrong about which side a fault came from
- What this page cannot tell you
- Common questions about which parent a fault came from
The short answer
Does it matter which parent a gene fault came from?
For most inherited cancer genes, no. A faulty copy behaves the same whether it came from your mother or your father, and carries the same raised risk either way. What tends to differ is which side of the family gets looked at closely, not how the gene itself works.
Why the father's side is so often overlooked
Families naturally focus on the side that has had visible illness. If the mother's relatives have had breast or ovarian cancer, that side gets discussed at every gathering, while the father's side may carry the exact same fault, silently, without anyone thinking to ask.
A small number of genes are the exception
A handful of genes sit on the sex chromosomes or are affected by which parent they came from in more complex ways. These are uncommon in cancer genetics, and your counsellor will tell you plainly if the gene named on your report is one of them.
Most inherited cancer risk does not care which parent it came from. Family attention usually does.What actually differs
If the gene behaves the same, what changes by side?
The biology is usually identical. What differs is entirely about attention, history and who gets asked the right questions.
Which relatives get asked about
A family tree built only from the side with visible cancer misses half the picture. A thorough counsellor asks about both sides equally.
Whether men are included at all
A father's side can carry the same fault linked to breast or ovarian cancer without a single man in that branch ever being affected, since men rarely develop those cancers even as carriers.
Cultural focus on marriage and disclosure
In some families, a fault on the father's side is discussed less openly, especially around marriage negotiations, which can leave that branch under-investigated for reasons that have nothing to do with biology.
Which relative gets offered testing first
Testing should follow whoever in the family already has cancer, not assumptions about which side looks more affected on the surface.
Not sure whether this applies to you?
Ask an oncologistTracing a fault properly
How a counsellor decides which side to look at
Ask about both sides equally
A proper family tree covers the mother's and the father's relatives in the same depth, going back at least two generations where possible.
Do not assume men are unaffected because they are healthy
Men are asked about specifically, since they can carry the same faults without developing the cancers most associated with them.
Test the parent, not just the child
If a child tests positive, testing both parents shows which side the fault travelled through, which then guides testing for that side's wider family.
Follow the confirmed side outward
Once a side is confirmed, aunts, uncles and cousins on that branch can be offered testing for that exact fault, rather than guessing.
On your report
Words this topic uses, in plain language
- Paternal side
- Your father's relatives: his parents, siblings and their children.
- Maternal side
- Your mother's relatives, traced the same way.
- Cascade testing
- Testing relatives one branch at a time, starting from a confirmed result and working outward through the family.
- Sex-linked gene
- A gene that sits on the X or Y chromosome, where inheritance patterns can differ by the child's sex. Most cancer genes are not sex-linked.
- Autosomal
- On one of the numbered chromosomes, not the X or Y. Most inherited cancer genes are autosomal, so the parent's sex does not change how the fault behaves.
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Side by side
Autosomal genes versus the rare sex-linked exceptions
Most cancer genes (autosomal)
Rare sex-linked exceptions
Behaves the same from either parent
Can behave differently depending on which parent it came from
Sons and daughters equally likely to inherit it
Sons and daughters can face different chances
Both parents' families should be traced equally
Tracing depends on the specific gene involved
The large majority of inherited cancer genes
Uncommon in cancer genetics; your counsellor will confirm if yours applies
Commonly believed
What families get wrong about which side a fault came from
"There's no cancer on my father's side, so it must come from my mother."
A fault can sit silently on the father's side for generations if the men who carry it are simply less likely to develop the cancers linked to it. Absence of illness is not absence of the fault.
"Breast and ovarian cancer genes only pass through women."
A man can carry and pass on these faults exactly as a woman can, and he carries a raised risk of his own, including of prostate and male breast cancer.
"My father's family won't want to discuss this."
That reluctance is common and understood, but it does not change the biology. A counsellor can often approach the conversation in a way that feels less exposing for the family.
"The side with more cancer cases is definitely the side the fault came from."
Visible cases point to where cancer has appeared, not necessarily to which side carries a genetic fault. Testing, not a head count, settles the question.
Being straight with you
What this page cannot tell you
It cannot tell you which side of your family carries a fault. That is answered by tracing the confirmed result of whoever in the family already tested positive, back through their parents.
It cannot tell you whether your specific gene is an exception
A small number of genes do behave differently depending on the parent. Whether the gene named on your report is one of them is a question for the counsellor who explained your result, not a general page like this one.
Who this does not apply to
If no gene fault has been confirmed anywhere in your family, this question does not yet apply to you. It becomes relevant only once a result exists and the family is working out how it arrived.
If you suspect your father's side has been left out of the conversation, call the helpline and say so. It is a common and reasonable thing to raise.Questions we are asked
Common questions about which parent a fault came from
Can a father pass on a breast cancer gene fault?
Yes, in exactly the same way a mother can. He also carries a raised risk himself, including of prostate and male breast cancer, and can pass the fault to a son or a daughter.
Why does my counsellor want to know about my father's side too?
Because most cancer genes are equally likely to travel through either side. Leaving out one parent's family is one of the most common ways an inherited pattern gets missed entirely.
If my mother's side has more cancer cases, does that mean it came from her?
Not necessarily. It may mean the fault happens to have caused more visible illness on that side, or that side has simply been discussed more. Testing traces the actual source.
Are there genes where the parent really does matter?
A small number of genes are affected by which parent they came from, or sit on the sex chromosomes, and can behave differently as a result. These are uncommon in cancer genetics, and your counsellor will tell you if yours is one.
How do we find out which side the fault came from?
By testing both parents of whoever tested positive. Whichever parent also carries the fault shows you which side of the family to focus on next.
What if both parents are unavailable to test?
A counsellor can sometimes work out the likely side from other relatives' history, though the answer is less certain without a direct test on a parent.
Does it matter for my own children which side it came from?
For most genes, no. What matters for your children is whether you yourself carry the fault, not which of your parents it came from.
Who can help us trace which side of the family is affected?
A genetic counsellor is trained to build out both sides of a family tree and interpret test results across it. 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
- Cancer Research UK — Inherited cancer genes and increased cancer risk
- 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?
- 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
Cancer risk from the father's sideA closer look at the side that is often overlookedCan a cancer gene skip a generation?Why an unaffected carrier parent can still pass on a faultWhy the risk is 50% for each childThe maths behind how a fault passes to each childCancer genetics explainedThe basics, if you are starting from the beginning
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