Sex linkage

Revision as of 16:00, 20 August 2012 by WikiBot (talk | contribs) (Robot: Automated text replacement (-{{SIB}} +, -{{EH}} +, -{{EJ}} +, -{{Editor Help}} +, -{{Editor Join}} +))
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

WikiDoc Resources for Sex linkage


Most recent articles on Sex linkage

Most cited articles on Sex linkage

Review articles on Sex linkage

Articles on Sex linkage in N Eng J Med, Lancet, BMJ


Powerpoint slides on Sex linkage

Images of Sex linkage

Photos of Sex linkage

Podcasts & MP3s on Sex linkage

Videos on Sex linkage

Evidence Based Medicine

Cochrane Collaboration on Sex linkage

Bandolier on Sex linkage

TRIP on Sex linkage

Clinical Trials

Ongoing Trials on Sex linkage at Clinical

Trial results on Sex linkage

Clinical Trials on Sex linkage at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Sex linkage

NICE Guidance on Sex linkage


FDA on Sex linkage

CDC on Sex linkage


Books on Sex linkage


Sex linkage in the news

Be alerted to news on Sex linkage

News trends on Sex linkage


Blogs on Sex linkage


Definitions of Sex linkage

Patient Resources / Community

Patient resources on Sex linkage

Discussion groups on Sex linkage

Patient Handouts on Sex linkage

Directions to Hospitals Treating Sex linkage

Risk calculators and risk factors for Sex linkage

Healthcare Provider Resources

Symptoms of Sex linkage

Causes & Risk Factors for Sex linkage

Diagnostic studies for Sex linkage

Treatment of Sex linkage

Continuing Medical Education (CME)

CME Programs on Sex linkage


Sex linkage en Espanol

Sex linkage en Francais


Sex linkage in the Marketplace

Patents on Sex linkage

Experimental / Informatics

List of terms related to Sex linkage

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Sex linkage is the phenotypic expression of an allele that is related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of expressing the trait. Since, in humans, there are many more genes on the X than there are on the Y, there are many more X-linked traits than there are Y-linked traits.

In mammals, the female is the homogametic sex, having two X chromosomes (XX), while the male is heterogametic, having one X and one Y chromosome (XY). Genes that are present on the X or Y chromosome are called sex linked genes.

X-linked recessive traits are expressed in all heterogametics, but only in those homogametics that are homozygous for the recessive allele. For example, an X-linked recessive allele in humans causes haemophilia. Haemophilia is much more common in males than females because males are hemizygous - they only have one copy of the gene in question - and therefore express the trait when they inherit one mutant allele. In contrast, a female must inherit two mutant alleles, a less frequent event since the mutant allele is rare in the population.

The incidence of recessive X-linked phenotypes in females is the square of that in males (squaring a proportion less than one gives an outcome closer to 0 than the original). If 1 in 20 males in a human population are green color blind, then 1 in 400 females in the population are expected to be color blind (1/20)*(1/20).

X-linked recessive inheritance
X-linked recessive inheritance

X-linked traits are maternally inherited from carrier mothers. Each son born to a carrier mother has a 50% probability of inheriting the X-chromosome carrying the mutant allele. There are a few Y-linked traits; these are inherited from the father.

In classical genetics, a reciprocal cross is performed to test if a trait is sex-linked.

X-linked recessive

X-linked inherited diseases occur far more frequently in males because they only have one X chromosome. Females must receive a copy of the gene from both parents to have such a recessive disease. However, they will still be carriers if they receive one copy of the gene. Recessive genes on the X chromosome that cause serious diseases are usually passed from female carriers to their ill sons and carrier daughters. This is because males, who always have the disease and are not just carriers, would have to father a daughter to pass on the gene. This is unlikely because severe genetic diseases often cause death in childhood or early adulthood. Even those males who survive childhood are unlikely to father children because a sickly male will be less likely to find a mate. However, if the disease shows up late in life, or is not severe, he will pass the gene to all of his daughters. He can not pass it to his sons because a male receives his X chromosome from his mother. A mother with one copy of the gene has a 50% chance of passing it to her children of both sexes, but her daughters will just be carriers of the gene unless their father has it too.

Diseases well known for their X-linked recessive inheritance are hemophilia (types A and B), and color blindness.

X-linked dominant

There are few examples of X-linked dominant diseases; the best known in this category is vitamin D resistant rickets. Other examples are:


  • Various failures in the SRY genes

cs:Dědičnost znaků a pohlaví it:Caratteri legati al sesso sr:Наслеђивање везано за X хромозом

Template:WH Template:WS