Lably
Skip to content

Haemophilia in European royalty

Genetic disorder in European royalty

  • 9 min read
  • 9 chapters

Related on Lably

Through Queen Victoria, Sex linkage and Dominance (genetics)

LabHeredity & GeneticsLab · Class 9–11Cell Cycle & Division

Genetic inheritance of haemophilia

The sex-linked X-chromosome bleeding disorder manifests almost exclusively in males, even though the genetic mutation causing the disorder is located on the X-chromosome and can be inherited from the mother by male children or from either mother or father by female children. This is because the trait is recessive, meaning that only one correctly functioning copy of the blood-clotting factor gene is necessary for normal clotting. Females have two X-chromosomes, and hence redundant copies of the blood-clotting factor gene located on them. A female who inherits a mutated copy on one X-chromosome has also inherited a second X-chromosome from the other parent that is likely to carry a non-mutated copy of the gene, capable of directing appropriate clotting. Such a female, with normal clotting but possessing a single mutated copy of the gene, is called a carrier. Males possess only a single X-chromosome, inherited from their mother, having received a Y-chromosome from their fathers instead of a second X. If their sole X-chromosome contains the haemophilia mutation they possess no second copy to provide for normal function, as in carrier females. Each child of a carrier will have a 50 percent chance of inheriting their mother's mutation, of being a haemophiliac (sons) or carrier (daughters). The daughter of a male haemophiliac will always inherit his mutation, while a son cannot ever inherit it. A female will be affected with haemophilia proper only in the rare circumstance that she inherits mutated X-chromosomes from both a haemophiliac father and a carrier or a haemophiliac mother. No case of such double inheritance is known among Queen Victoria's descendants, although there has been at least one symptomatic carrier.

Although an individual's haemophilia can usually be traced in the ancestry, in about 30 percent of cases, there is no family history of the disorder, and the condition is speculated to be the result of spontaneous mutation in an ancestor. Victoria's appears to have been a spontaneous or de novo mutation, most likely inherited from one of her parents, and she is usually considered the source of the disease in modern cases of haemophilia among her descendants. Queen Victoria's mother, Victoria, Duchess of Kent, was not known to have a family history of the disease, although it is possible that she was a carrier, but among her three children only Victoria received the mutated copy. Queen Victoria's father, Prince Edward, Duke of Kent, was not a haemophiliac, but the mutation may have arisen as a germ-line mutation within him. The rate of spontaneous mutation is known to increase with paternal age (and is higher in fathers than in mothers at all ages); Victoria's father was 51 at her birth. The probability of Victoria's mother having had a lover with haemophilia is minuscule, given the low life expectancy of early 19th-century haemophiliacs, as well as the otherwise low possibility of illegitimacy in this instance.

Sign in to keep reading

8 more chapters are free with a Lably account.

More in Human body

Anatomical terms of locationStandard terms for unambiguous description of relative placement of body partsPrefrontal cortexPart of the brain responsible for personality, decision-making, and social behaviorPubMedOnline biomedical databaseMucous membraneProtective layer that lines the interior of hollow organsNeuroimagingSet of techniques to measure and visualize aspects of the nervous systemNeuroscientistIndividual who studies neuroscience