Visual communication aid: X-linked recessive inheritance

There are two communication aids available to view and download (.pdf):

• X-linked recessive inheritance: affected father
• X-linked recessive inheritance: carrier mother

Double-sided printing in colour is recommended (but not required). All content is also included below in an accessible format.

More information about these and other VCAs is available in this article.

We all have over 20,000 genes, which provide instructions for how our body works.​ Our genes are packaged into structures called chromosomes. ​Our chromosomes come in pairs, with one inherited from each parent. ​

Most chromosomes (the autosomes) are numbered 1–22. Our sex chromosomes are called X or Y, and usually determine sex assigned at birth.​

• Females typically have two X chromosomes.
• Males typically have one X and one Y chromosome​.

X-linked recessive conditions are caused by changes in genes that are located on the X chromosome.

Males who have a change on their X chromosome would be expected to develop the condition.

Females who have a change on one of their two copies of the X chromosome are knowns as carriers. Usually, they would not develop the condition. In some cases, they may develop a milder version of the condition.

When an affected male has a child with someone who is not a carrier, male children will inherit their Y chromosome and female children will inherit their X chromosome with the change.​

This means, for every pregnancy (figure 1):​

• All male children will be unaffected and not carriers of the condition.
• All female children will be carriers for the condition and usually unaffected.

When a female carrier has a child with someone who is not affected by the condition, either the X chromosome with the change or the X chromosome without the change will be inherited by the child.

Figure 1: X-linked recessive inheritance when the father is a affected by the condition

When a female carrier has a child with someone who is not affected by the condition, either the X chromosome with the change or the X chromosome without the change will be inherited by the child.

This means, for every pregnancy (figure 2):​

• There is a 25% (1 in 4) chance of having a female carrier child (like their mother)​.
• There is a 25% (1 in 4) chance of having a female unaffected child, who is not a carrier​.
• There is a 25% (1 in 4) chance of having a male child affected with the condition​.
• There is a 25% (1 in 4) chance of having a male child who is not affected with the condition.

Figure 2: X-linked recessive inheritance when the mother is a carrier of the condition

• Gene change:​ Changes in a gene or chromosome used to be referred to as ‘mutations’. Now, they are more commonly called changes, alterations or variants.

For patients

• NHS England Genomics Education Programme: X-linked recessive inheritance (where the father has a condition) animation