[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Genetic disease](https://durgical.com/en/general-pathology/#a-genetic) › Mendelian inheritance: autosomal dominant, recessive and X-linked

[General pathology](https://durgical.com/en/general-pathology/) · [Genetic disease](https://durgical.com/en/general-pathology/#a-genetic)

# Mendelian inheritance: autosomal dominant, recessive and X-linked

- Topic

When a disease depends on a single gene, it passes through families in predictable patterns that let us estimate each child's risk.

Updated 2026-11-01

## Key points

- Autosomal dominant: vertical transmission, both sexes, a one-in-two risk for each child of an affected parent.
- Autosomal recessive: healthy carrier parents, a one-in-four risk per pregnancy; more common with consanguinity.
- X-linked recessive: almost only males; never passed from father to son; daughters of an affected man are obligate carriers.
- Dominant disorders usually hit receptors and structural proteins; recessive disorders usually hit enzymes.
- Incomplete penetrance and variable expressivity are typical of dominant disorders (neurofibromatosis type 1, Marfan).

## What it is

Single-gene disorders follow Mendel's laws: the gene lies on an autosome or on the X chromosome, and either one altered copy is enough (dominant) or two are needed (recessive). Recognising the pattern in a pedigree guides diagnosis, genetic counselling and testing of relatives.

## Key facts

- New (de novo) mutation: a child with a dominant disease may have healthy parents; this is the case in most achondroplasia and is linked to older paternal age.
- Pleiotropy: one gene affects several organs (Marfan: eye, aorta and skeleton).
- Locus heterogeneity: different genes cause the same picture; allelic heterogeneity: different mutations in the same gene.
- Codominance: both alleles are expressed, as in blood group AB.
- In females, random inactivation of one X explains why some carriers have mild symptoms.

## Single-gene inheritance patterns

| Pattern | Who is affected | How it is passed on | Examples |
| --- | --- | --- | --- |
| Autosomal dominant | Both sexes equally; seen in every generation | One affected parent; each child has a one-in-two chance | Marfan, familial hypercholesterolaemia, Huntington, adult polycystic kidney disease, achondroplasia |
| Autosomal recessive | Both sexes; siblings in one generation | Two healthy carrier parents; one in four children affected | Cystic fibrosis, sickle cell disease, phenylketonuria, Tay-Sachs |
| X-linked recessive | Almost only males | Carrier mother: half of her sons affected; no male-to-male transmission | Duchenne muscular dystrophy, haemophilia A and B, G6PD deficiency |
| X-linked dominant | Both sexes; females milder | Affected father: all of his daughters and none of his sons | X-linked hypophosphataemic rickets |
| Mitochondrial | Both sexes | Only through the mother; very variable expression (heteroplasmy) | MELAS, Leber hereditary optic neuropathy |

## Clinical notes

- In a pedigree, a disease that ‘skips’ generations suggests recessive inheritance or incomplete penetrance.
- Genetic counselling uses the pattern to estimate risk; molecular testing of the gene confirms it.

## Memory aid

Dominant runs down the family tree, recessive hides among siblings, X-linked travels through mothers and lands on sons.

## Test yourself

Think of the answer, then tap the question to see it.

## Which pedigree feature rules out X-linked inheritance?

Father-to-son transmission: a father passes his Y chromosome, not his X, to his sons.

## Two parents who carry cystic fibrosis: what is their risk in each pregnancy?

One in four of an affected child, one in two of a carrier child and one in four of a non-carrier.

## Why can a child with achondroplasia have parents of normal height?

Because most cases come from a new mutation in the FGFR3 gene rather than from an affected parent.

## Which kind of protein is usually defective in autosomal recessive diseases?

Enzymes: half of the normal activity is enough to work, which is why carriers are healthy.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/general-pathology/mendelian-inheritance-autosomal-dominant-recessive-and-x-linked/)

## Related

- [How a single gene causes disease: enzymes, receptors and structural proteins](https://durgical.com/en/general-pathology/how-a-single-gene-causes-disease-enzymes-receptors-and-structural-proteins/)
- [Nonclassic inheritance: repeat expansions, mitochondrial genes, imprinting, mosaicism](https://durgical.com/en/general-pathology/nonclassic-inheritance-repeat-expansions-mitochondrial-genes-imprinting-mosaicis/)
- [Multifactorial (complex) disorders](https://durgical.com/en/general-pathology/multifactorial-disorders/)
- [Chromosome abnormalities: number and structure](https://durgical.com/en/general-pathology/chromosome-abnormalities-number-and-structure/)

## Related conditions

- [Marfan syndrome](https://durgical.com/en/conditions/marfan-syndrome/)
- [Cystic fibrosis](https://durgical.com/en/conditions/cystic-fibrosis/)
- [Duchenne muscular dystrophy](https://durgical.com/en/conditions/duchenne-muscular-dystrophy/)
- [Haemophilia A and B](https://durgical.com/en/conditions/haemophilia-a-and-b/)
- [Familial hypercholesterolemia](https://durgical.com/en/conditions/familial-hypercholesterolemia/)
- [Huntington disease](https://durgical.com/en/conditions/huntington-disease/)
- [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/)
- [Autosomal dominant polycystic kidney disease](https://durgical.com/en/conditions/autosomal-dominant-polycystic-kidney-disease/)
- [Achondroplasia](https://durgical.com/en/conditions/achondroplasia/)
- [Neurofibromatosis (types 1 and 2)](https://durgical.com/en/conditions/neurofibromatosis/)
- [Glucose-6-phosphate dehydrogenase (G6PD) deficiency](https://durgical.com/en/conditions/glucose-6-phosphate-dehydrogenase-deficiency/)
- [Phenylketonuria (PKU)](https://durgical.com/en/conditions/phenylketonuria/)

## Elsewhere in DurgiPedia

- [Types of mutations](https://durgical.com/en/biochemistry/topics/types-of-mutations/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [What are the different ways a genetic condition can be inherited?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/inheritance/inheritancepatterns/) (MedlinePlus, US National Library of Medicine, 2026); [Marfan syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/marfan-syndrome/) (MedlinePlus, US National Library of Medicine, 2026); [Duchenne and Becker muscular dystrophy: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/duchenne-and-becker-muscular-dystrophy/) (MedlinePlus, US National Library of Medicine, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/general-pathology/mendelian-inheritance-autosomal-dominant-recessive-and-x-linked/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/mendelian-inheritance-autosomal-dominant-recessive-and-x-linked/