Autosomal inheritance occurs when a parent passes down a condition to a child via autosomes, which are a type of chromosome. Chromosomes are thread-like structures inside cells. They contain DNA, which tells the body how to grow and function.

Humans generally have 23 pairs of chromosomes. One pair determines a person’s sex. The other 22 are autosomes, which influence other aspects of development. If one or both parents have an altered autosome, their child will inherit it.

Whether this causes the child to have a genetic condition depends on the condition itself. In some cases, for a child to inherit a condition, both parents must carry the autosome that causes it. In other cases, a child can inherit a condition when only one parent carries the autosome.

Read on to learn more about autosomal inheritance, dominant and recessive types, and the conditions people can inherit via autosomes.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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The term “autosomal” refers to autosomes, which are a type of chromosome.

Humans have 23 pairs of chromosomes, 22 of which are autosomes. The remaining pair are sex chromosomes, which determine a person’s sex.

Autosomes consist of strands of DNA. DNA has regions known as genes, which tell cells how to grow and function. If a person has an autosomal condition, it means they have a health condition that has occurred as a result of a change in one of these genes.

Scientists have assigned each autosome a number that corresponds to its size. The largest autosome, chromosome 1, has 2,800 genes, while the smallest, chromosome, 22, has 750 genes.

People inherit genetic traits from their parents. This occurs during conception, when sperm from one parent joins the egg, or ovum, of another.

Each of these cells contains a full set of chromosomes and genes, which means that each person inherits two copies of both. These chromosomes and genes contain all the information necessary to create another human.

Sometimes, genes can change, producing a gene variant. Some of these changes are so minor that they do not affect the way a gene works. However, if the changes are large enough, they can affect a gene’s function and result in disease.

While inherited genes can influence health conditions, it is also possible for genes to change in the uterus while a fetus is developing. This can result in a child having a genetic condition even though there is no family history of it.

Additionally, family members who inherit the same gene variant do not always have the same symptoms. This is because there is a relationship between environment and genetics, which influences whether a gene is switched “on” or “off.” This is known as gene expression.

There are two main subtypes of autosomal inheritance: dominant and recessive.

Autosomal dominant means that inheriting a single copy of a gene variant is enough to cause the condition. In this scenario, a child has a 50% likelihood of inheriting the gene variant from one parent and having the condition.

In contrast, autosomal recessive means that, in order to have a certain health condition, a child needs to inherit two copies of the gene that causes it — one from each parent.

If both parents are carriers but do not have the autosomal recessive condition themselves, their child has a 25% likelihood of inheriting the condition.

In addition to these inheritance patterns, there are other ways people can inherit genetic diseases:

  • X-linked dominant: These conditions stem from gene variants on the X chromosome, which determines sex. Males have only one X chromosome, so inheriting one copy of the variant gene causes the condition. In females, who have two X chromosomes, the symptoms may be less severe. Only females can pass on X-linked disorders.
  • X-linked recessive: As with X-linked dominant, inheriting one copy of the variant gene causes the condition in males. However, in females, two copies of the variant gene are necessary to cause the condition.
  • X-linked: These conditions stem from variants on the X chromosome, but they are not clearly dominant or recessive.
  • Y-linked: These conditions stem from variants on the Y chromosome. Only males have a Y chromosome, so these conditions pass from a male parent to a male child.
  • Codominant: In these disorders, two gene variants produce different effects, but both can influence or determine a health condition.
  • Mitochondrial: The mitochondria are cell structures that produce energy, but they also contain a small amount of DNA. A female parent, but not a male parent, can transmit a gene variant from mitochondria.

Here are some examples of autosomal dominant conditions:

Here are some examples of autosomal recessive conditions:

  • cystic fibrosis, which causes mucus buildup in the lungs and digestive system
  • sickle cell disease, a group of conditions that change the shape of red blood cells
  • Tay-Sachs disease, in which the enzyme that assists in breaking down fatty substances is absent
  • phenylketonuria, a condition that makes a person unable to metabolize phenylalanine, which can cause brain and nerve damage

There are several ways to test for autosomal traits:

  • Single-gene tests: These detect variations in one specific gene. Doctors may recommend one if they suspect that a person has a certain inheritable condition.
  • Panel tests: These identify variations in many genes that affect a certain aspect of health. For example, one panel test may target genes that affect the nervous system, while another may assess genes that affect cancer risk.
  • Large-scale genetic tests: There are two types of large-scale genetic tests. Genome sequencing examines a person’s entire DNA, not just the genes. Exome sequencing examines either all the genes in the DNA or only the genes related to someone’s medical condition.

Some tests look for genetic expression changes as well. In addition to being completely “on” or “off,” genes can have different levels of expression in different types of cells. Gene expression tests compare these levels in healthy and diseased cells.

In addition to gene tests, there are tests for chromosomal changes.

If a person suspects they or their child could carry the gene for an autosomal condition, they may wish to ask their doctor any of the following questions:

  • What is my risk of having a genetic condition?
  • Could a disease that runs in my family have a genetic cause?
  • What is my risk of passing on a genetic condition to my child?
  • Should I get genetic testing?
  • If I want to have a baby, should my partner and I get genetic testing first?
  • Is there a way to minimize the risk of developing the condition, such as by avoiding environmental risk factors?
  • If I or another family member has the condition, what treatments are available?

Autosomal inheritance is a way for genetic conditions to pass from parent to child. It describes genetic variants that sit within one of the autosomes, which are a type of chromosome.

In autosomal dominant inheritance, a child needs only one copy of a gene variant to develop a condition. For this to happen, only one parent needs to carry the gene.

In autosomal recessive inheritance, a child needs two copies of a gene variant — one from each parent — to develop a condition.

Huntington’s disease, cystic fibrosis, and sickle cell anemia are examples of conditions with autosomal inheritance. If a person is concerned that they or their child may carry the genes for these conditions, they should speak with a doctor.