When a condition runs in a family, or a child is born with a condition neither parent has, the explanation usually comes down to how genes are passed from parent to child. Genes sit on chromosomes, and each person typically inherits one copy of most genes from their mother and one from their father. Whether a condition appears, and in whom, depends heavily on which inheritance pattern is at work.
This page walks through the major single-gene inheritance patterns at a plain-language level: autosomal dominant, autosomal recessive, X-linked, de novo variants, and genomic imprinting. Each section links to a dedicated page with more detail. It is meant as an orientation, not a diagnosis. For a specific family history or a specific condition, a genetic counselor or clinician is the right next step.
Autosomal dominant: one altered copy is enough
Most genes come in two copies, one inherited from each parent. In autosomal dominant inheritance, a change in just one of those two copies is enough to cause the condition. A person with an autosomal dominant condition often has an affected parent, and each of their own children has roughly a 1 in 2 chance of inheriting the altered copy, in every pregnancy. In other cases, the condition traces back to a brand-new change in the gene rather than one inherited from either parent, so it can appear with no family history at all.
Autosomal recessive: it takes two altered copies
In autosomal recessive inheritance, a person is affected only when both copies of a gene carry a change, one inherited from each parent. Someone with just one altered copy is usually called a carrier. Carriers typically do not have signs or symptoms of the condition themselves, because their one working copy of the gene is enough. This is why autosomal recessive conditions can seem to skip generations: two unaffected carrier parents can each pass down their altered copy, and a child who receives both is affected, while the parents and most relatives show nothing.
X-linked: genes on the X chromosome
Some genes sit on the X chromosome, one of the two sex chromosomes. Because males typically have one X chromosome and females typically have two, a change on the X chromosome tends to affect males more often, and often more severely, than females. A female with one altered copy and one working copy of the gene may have mild symptoms or none at all, since the working copy can often compensate, while a male with the same altered copy on his only X chromosome usually shows the full condition. The X-linked inheritance page covers how these patterns play out across a family tree, including why fathers do not pass X-linked traits to their sons.
De novo variants: a change that starts with this child
Not every genetic condition is inherited from a parent. A de novo variant is a new genetic change that appears for the first time in a child, found in the child's cells but not in either parent's. This happens because egg and sperm cells, and the early cell divisions after fertilization, are not perfectly error-free copying processes. A de novo variant can produce a condition that typically is inherited, but in this particular family it starts fresh, with no prior family history to point to.
Genomic imprinting: some genes only work from one parent's copy
Most genes are active whether they came from the mother's copy or the father's copy. A smaller set of genes are different: through a process called genomic imprinting, one parent's copy of the gene is chemically silenced, so only the other parent's copy is normally active. When something disrupts that balance, such as losing the active copy or inheriting both copies from a single parent (known as uniparental disomy), a person can end up with no working copy of an important gene at all, even though the gene itself was not mutated. The genomic imprinting page goes into how this differs from ordinary dominant or recessive inheritance.
Comparing the patterns at a glance
| Pattern | How it works | Example |
|---|---|---|
| Autosomal dominant | One altered gene copy is enough to cause the condition | Huntington's disease |
| Autosomal recessive | Both gene copies must be altered; carriers with one copy are usually unaffected | Cystic fibrosis |
| X-linked | The gene sits on the X chromosome; effects often differ between males and females | Hemophilia |
| De novo variant | A new change appears in the child, not found in either parent | Varies by condition |
| Genomic imprinting | Only one parent's copy of certain genes is normally active | Varies by chromosome region affected |
Many common health conditions, such as heart disease or type 2 diabetes, do not follow any single one of these patterns. They result from the combined effect of many genes together with lifestyle and environmental factors, which is a different kind of inheritance question than the single-gene patterns covered here.
Finding a specific condition
This page is a map, not a destination. To look up how a specific diagnosed condition is inherited, the conditions index lists the conditions covered on this site by category. For what inheritance means for a specific family, including the chance a future child could be affected, a genetic counselor can walk through the testing and counseling process in detail. Unfamiliar terms along the way are collected in the glossary.
Educational, not diagnostic: this page explains general inheritance concepts. It is not a substitute for genetic testing, a formal pedigree analysis, or advice from a qualified clinician about any individual or family.