Inheritance, family risk and prenatal testing
How conditions are passed down through a family, what each pregnancy test can actually tell you, and what a reported probability means for you. Written for families who need to decide, not for an exam.
A screening result is not a diagnosis, and the fraction you were given — 50%, 25%, one in three — is rarely your own chance. These guides separate the three questions that get blurred together: what can be passed down, what a pregnancy screen is actually looking for, and which test can give a definite answer.
How inherited conditions run in families
Autosomal dominant and recessive, X-linked, Y-linked and mitochondrial inheritance — explained from the pedigree, not from a syllabus.
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Autosomal Dominant Inheritance: What a 50% Chance Means
If one parent has a dominant condition, each child has a 50% chance of inheriting the gene change. What that 50% covers, what it does not, and why your own chance is usually lower.
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Autosomal Recessive Inheritance: Two Carriers, 25% Chance
Two healthy parents, a 25% chance in every pregnancy, and usually no family history at all. How recessive conditions are passed on, and what the chances are for each relative.
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X-Linked Recessive Inheritance: Why It Affects Boys
A carrier mother passes an X-linked condition to half her sons and carrier status to half her daughters. A father passes it to none of his sons. The rules, and the exceptions.
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Mitochondrial Inheritance: Why It Comes From the Mother
Mitochondrial conditions are passed on by mothers, never by fathers. How to spot the pattern in a family tree, and why brothers and sisters can be affected so differently.
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X-Linked Dominant vs Recessive: What Is the Difference?
Both patterns travel on the X chromosome and neither passes from father to son. The difference is what one changed X does in a daughter — and it changes the whole family tree.
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Y-Linked Inheritance: Father to Son, and Why It Is Rare
A Y-linked gene change passes from father to every son and to no daughter. How to recognise the pattern, and why true examples in people are far rarer than textbooks suggest.
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De Novo Mutation: What It Means and Can It Happen Again?
A de novo gene change is new in the child and not inherited from either parent. Why the chance for another baby is usually quoted as 1–2%, and when it is higher or lower.
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Can a Genetic Disease Skip a Generation? Which Ones Do and Why
Some do. X-linked conditions pass through healthy daughters, recessive ones through carriers, and some dominant genes spare a carrier. Which fits your family?
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Someone in my family has it. How is my chance calculated?
The family-risk questions people actually arrive with, with the numbers derived in front of you and the factors that move them.
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My Parent Has Huntington's: What Are My Chances?
A child of a parent with Huntington's disease starts at a 50% chance. Why your chance today is lower, how your age changes it, what the CAG numbers mean, and what testing involves.
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First Cousins Having a Baby: What Are the Real Risks?
In any pregnancy the chance of a serious genetic or congenital condition is about 2–3%. For first cousins it is roughly double, about 4–6%. What that means in practice, and what changes it.
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My Sibling Has a Genetic Condition — Am I a Carrier?
If your brother or sister has a recessive condition and you are healthy, your chance of being a carrier is 2 in 3, not 1 in 2. Why — and what it means for your own children.
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My Parent Has a BRCA Mutation: What Does It Mean for Me?
If a parent has a pathogenic BRCA1 or BRCA2 variant, each child has a 50% chance of inheriting it. Inheritance is not the same as lifetime breast or ovarian cancer risk.
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Lynch Syndrome in the Family: What Are My Chances?
Which family history patterns point to Lynch syndrome, who should be tested first, and why a confirmed gene change gives each child a 50% chance of inheriting it.
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My Sibling Has Cystic Fibrosis: Am I a Carrier?
If your brother or sister has cystic fibrosis and you do not, your chance of being a carrier is 2 in 3. Where that comes from, and which CFTR test gives a clear answer.
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Both Parents Have Sickle Cell Trait: What Are the Chances?
If both parents have sickle cell trait, each child has a 25% chance of sickle cell disease. What changes when one parent carries haemoglobin C or beta-thalassaemia instead.
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Hemophilia Inheritance: The Chances for Sons and Daughters
A simple hemophilia inheritance chart. Compare a carrier mother with an affected father, and see what each means for sons and for daughters.
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My Brother Has Duchenne: Am I a Carrier?
Duchenne carrier testing for mothers and sisters: where the one-in-three estimate comes from, what a mother's negative result means, and why carriers need heart checks.
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Diabetes, Alzheimer’s, cancer, schizophrenia: is it hereditary?
The conditions most families have already seen. What a parent’s or sibling’s diagnosis does to your own chance, and the signs that it is a single gene after all.
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Is Type 2 Diabetes Hereditary? Your Risk If a Parent Has It
About 1 in 3 adults get type 2 diabetes. With one affected parent it is roughly 40–50%, with both about 2 in 3. What moves your own number, and what lowers it.
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Is Alzheimer's Hereditary? Your Risk If a Parent Had It
A parent or sibling with Alzheimer's roughly doubles your risk, yet most people never develop it. When the age it started points to a 50% gene instead.
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Is Cancer Hereditary? When a Family History Points to a Gene
Only 5–10% of cancers are inherited, but a close relative with breast, bowel or prostate cancer roughly doubles your risk. The signs it is a gene, and what to do.
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Is Schizophrenia Hereditary? Your Risk If a Parent or Sibling Has It
About 1 in 100 people develop schizophrenia; with one affected parent, about 1 in 10; with both, roughly 1 in 3. Why age matters, and what it means for children.
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Screening and diagnostic tests in pregnancy
What NIPT, carrier screening, CVS and amniocentesis can each tell you, when they are usually done, and what follows an unexpected result.
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Prenatal Testing Timeline: What Happens in Each Week
When NIPT, the 12-week scan, CVS, the quad screen, amniocentesis and the 20-week scan usually happen in pregnancy — and what each one can actually tell you.
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Screening vs Diagnostic Tests in Pregnancy: The Difference
Why NIPT, blood tests and ultrasound are screening tests that estimate a chance, while CVS and amniocentesis can actually diagnose certain genetic conditions.
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What Does NIPT Test For — and What Can It Miss?
NIPT screens a maternal blood sample for a small set of chromosome conditions, including trisomy 21, 18 and 13. What is on the panel, what is not, and what a low-risk result does not rule out.
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High-Risk NIPT Result: What Happens Next?
A high-risk NIPT is a screening result, not a diagnosis. How likely it is to be confirmed, what the ultrasound can and cannot tell you, and what the next tests are.
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Low Fetal Fraction: Why Your NIPT Gave No Result
A no-result NIPT is neither positive nor negative. Why low fetal fraction happens, why it should not be filed as low risk, and what the options are next.
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NIPT vs the NT Scan: Do You Need Both?
NIPT and the nuchal translucency scan answer different questions. How they compare, what each one misses, and what to do when the two results disagree.
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Carrier Screening in Pregnancy: What It Tests and When
Carrier screening checks whether you and your partner could pass on a genetic condition. What is on the panels, why partner testing matters, and what a negative result really means.
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Positive Carrier Screen: Does My Partner Need Testing?
One positive carrier result rarely tells you the baby's risk on its own. When partner testing is needed, what happens if you both carry it, and what a negative partner result leaves.
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CVS vs Amniocentesis: Timing, Results and Risks
Compare CVS and amniocentesis: when each is done, what sample it takes, what the results can tell you, and why the placenta sometimes decides which one you are offered.
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Amniocentesis: Miscarriage Risk, Results and Recovery
What happens during an amniocentesis, why the miscarriage figures you read differ so much, how long results take, and which symptoms afterwards need urgent advice.
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