How is hemophilia inherited?

Answer 1

Hemophilia is carried on the X chromosome.

If hemophilia is inherited by a son (1/3 of the cases are spontaneous mutations and not inherited) the gene was passed to him from the mother.

If hemophilia is inherited by a daughter the gene could have come from either the mother, father or even both. (if from the father, he himself would have been a hemophiliac)

A male only has one X chromosome so if the one he has has the gene for hemophilia he is a hemophiliac.

The trait is considered recessive however incomplete dominance is know to occur frequently leading to the trait to at least partially be shown in females with a mutation on only one of their X chromosomes. When this occurs, women can demonstrate the symptoms and have low clotting factor levels similar to their male counterparts.

A female with the genes for hemophilia on both X chromosomes will undoubtably have hemophilia as well.

Answer 2

The genetic mutations responsible for causing hemophilia are found on the X chromosome. This means that a son (since he has only one X chromosome and gets it from his mother) can inherit the gene only from his mother if she has the mutation on one or both X chromosomes. Daughters can inherit the gene from their mother as well however are typically less symptomatic than their male counterparts since they have two X chromosomes. If the mother only has the mutation on one X chromosome, then all of her children, regardless of sex would have a 50% chance of receiving the mutation. If both of the mother's X chromosomes have the mutation the all on her children would inherit the gene. A father (who would be a hemophiliac himself) would pass the gene to all of his daughters and none of his sons (since any sons he had would receive his Y chromosome and not his X).