X-linked Inheritance

What are genes and chromosomes?

Every cell in the human body has 23 pairs of chromosomes. One of these pairs is made up of 2 sex chromosomes. These are called X and Y chromosomes. One of these is inherited from the mother and the other from the father. Females have 2 X chromosomes, while males have 1 X and 1 Y chromosome.

Chromosomes are made of genes. Genes are the blueprints for making proteins. These are the substances our bodies need to form and work well. The genes on the Y chromosome don’t exactly match up with the genes on the X chromosome.

What are mutations?

A mutation is a change in a gene that keeps it from working the way it should. Mutations in genes (genetic mutations) are inherited from our biological parents in certain ways. One of the common patterns of genetic inheritance is called X-linked inheritance. These mutations are passed on through the X chromosome.

What is X-linked inheritance?

X-linked inheritance means that the genetic mutation is located on the X chromosome. These mutations can cause X-linked disorders. X-linked mutations don't cause the same problems in males and females.

Mutations in genes on the X chromosome can be recessive or dominant.

Recessive X-linked disorders

In females, the normal, unchanged, or healthy gene can override a recessive mutation so the disorder is suppressed. Disorders linked to X-linked recessive mutations usually only happen in females when they have 2 copies of the recessive mutation (1 on each X chromosome). In this case, there's no dominant "healthy" gene to override it.

But, in males, there's only 1 X chromosome and if it has the recessive mutation, they will have the disorder.

Recessive X-linked disorders tend to be more common in males, because it's less likely that a female will get 2 copies of the recessive mutation.

Dominant X-linked disorders

In females, dominant X-linked mutations will always cause the disorder. This is because the mutated gene takes over or overrides the genes on the healthy X chromosome.

In males, remember, there's only 1 X chromosome and if it has the dominant mutation, they'll have the disorder.

In most dominant X-linked disorders, males have worse symptoms than females.

To date, there haven’t been any genes linked to cancer found on the X chromosome.