Skip main navigation
We use cookies to give you a better experience, if that’s ok you can close this message and carry on browsing. For more info read our cookies policy.
We use cookies to give you a better experience. Carry on browsing if you're happy with this, or read our cookies policy for more information.

Skip to 0 minutes and 13 secondsYou will remember from previous tutorials that women have two X chromosomes and men have an X and a Y chromosome. X-linked recessive inheritance occurs when there is a mutational deletion affecting one or more genes on the X chromosome. Because a woman has two X chromosomes, even if there was a gene mutation on one copy, the other, normal copy means that she is not usually severely affected with an X-linked condition. However, the situation is slightly complicated by X inactivation. Normally in cells, only one of the two X chromosomes is expressed. This is usually a random process, with 50-50 expression.

Skip to 0 minutes and 47 secondsHowever, if there's skewing towards the X chromosome with the gene mutation, it is possible that a female may show features of the associated conditional disease, although not usually as severely as in the males. As males only have one X chromosome, unlike the females, they will usually manifest the features of an X-linked condition. In X-linked inheritance, where the mother is a carrier and the father does not have an X-linked condition, there are four possible outcomes, each with a 25%, or one-in-four, chance. If the child inherits her father's X chromosome, she will be a girl. If she also inherits from her mother the X chromosome with the normal copy of the gene, she will not be a carrier.

Skip to 1 minute and 25 secondsHowever, if she inherits the X chromosome with the mutated gene, she will be a carrier, just like her mother. Therefore the daughter of a female carrier has a one-in-two chance of either being a carrier or not. If the child inherits the father's Y chromosome, he will be a boy. He also has a one-in-two chance of either inheriting the X chromosome with the normal gene and a one-in-two chance for inheriting the mutated copy of the gene and developing the X-linked condition.

Skip to 1 minute and 52 secondsWhere a father has an X-linked condition, remembering that he will pass on his X chromosome to his daughters and his Y chromosome to his sons, all his daughters will be carriers for the X-linked condition, and none of his sons will be affected. It is therefore not surprising that one of the defining features of an X-linked recessive pedigree is the lack of male-to-male transmission. In addition, affected individuals are usually male and related through unaffected females. In the next step, you'll be introduced to an X-linked recessive condition-- Duchenne muscular dystrophy. Duchenne muscular dystrophy is a devastating condition that causes progressive muscular weakness and is usually diagnosed in early childhood when motor milestones are delayed.

X-linked Recessive Inheritance

In this video, we learnt about X-linked recessive inheritance.

X-linked recessive conditions are caused by a gene alteration on the X chromosome. As males have only one X chromosome, if they have a gene alteration on their X chromosome they will develop the condition.

Females rarely show signs of X-linked recessive conditions as they usually have a second unaltered copy of the gene on their other X chromosome to compensate for an altered gene. A female who has a gene alteration on one of her X chromosomes is said to be a carrier for the X-linked recessive condition.

Features of X-linked recessive inheritance include:

  • Males are affected almost exclusively.
  • The gene mutation can be transmitted from female carriers to sons.
  • Affected males cannot transmit the condition to their sons.

A pedigree depicting x-linked recessive inheritance An example family pedigree depicting X-linked recessive inheritance

In the next step you will be introduced to an X-linked recessive condition, Duchenne Muscular Dystrophy, caused by a mutation / deletion affecting the dystrophin gene.

Image ©“Nick van Steendelaar” by Partij van de Arbeid. Licensed by CC BY 2.0

Share this video:

This video is from the free online course:

The Genomics Era: the Future of Genetics in Medicine

St George's, University of London

Get a taste of this course

Find out what this course is like by previewing some of the course steps before you join:

  • Welcome to Week 1
    Welcome to Week 1

    In this video, Lead Educator, Dr Kate Tatton-Brown welcomes learners to the course and explains the course aims and outcomes.

  • Did you know?
    Did you know?

    Our resident scientist tells you his favourite genomics facts.

  • Errors in recombination
    Errors in recombination

    This video describes how structural chromosome abnormalities occur when errors occur in recombination.

  • Responsibility in the genomic era
    Responsibility in the genomic era

    In this tutorial, you will hear from Dr Carwyn Rhys Hooper on the concept of responsibility for health.

Contact FutureLearn for Support