What is the inheritance pattern of hemophilia?

Hemophilia is X-linkes. That means that the defecct gene for both Hemophilia A and B is on the X-chromosome. Man have one X-chromosome, women two.

So, men who have the defect gene are ill, because they have only one copy (which is defect). Women have two copies, so they are usually not ill (unless they have two defect copies which is very rare). However, women can pass the defect copy to their sons (and daughters). The sons will be ill with a chance of 50%, the daughters will be healthy but will be carriers with a chance of 100%.

It's a bit complicated. Hope, I could explain it though.

for every disease, doctors say that there is 1 in 4 chance of getting the disease if one parents is a carrier of this condition or if the person has this disease. now if both parents are carriers or have this disease, there is 1 in 4 cahnce that the baby will not be like them. but anyway this is theoritically, so no one can actually say about the pattern.

I'm not sure but I don't thing being Gay is inherited.

Inheritance of Hemophilia

Hemophilia occurs when an individual cannot make enough of one of two blood-clotting proteins: Factor VIII or Factor IX. The instructions for how to make these proteins are found on a gene. If the structure of the gene is changed in any way, the gene is referred to as being mutated. A mutated gene does not have the correct instructions; and therefore either no protein or not enough protein is made.

The genes for Factor VIII and Factor IX are located on one of the sex chromosomes, the X chromosome. These genes and all of the other genes on the X chromosome are referred to as being X-linked. Females have two copies of the X chromosome; therefore they have two copies of any gene that is located on the X chromosome. A female can have two normal copies of the gene, one normal and one mutated gene, or two mutated genes. Males have only one X chromosome, so they only have one copy of a gene that is located on the X chromosome. (They also have a Y chromosome, which for the most part has different genes.) The gene on the X chromosome can be either normal or mutated.

If a male has a 鈥渘ormal鈥?Factor VIII or IX gene, then he does not have hemophilia. If, however, he has a mutated gene, he will have a bleeding disorder. In order for a female to have hemophilia, she must have two copies of the mutated gene. This is a rare situation. More common is when a female has one 鈥渘ormal鈥?copy of the Factor VIII or IX gene, and one mutated copy. She does not have hemophilia; instead she is called a carrier, because one of her X chromosomes carries the mutated gene. Her other X chromosome has a 鈥渘ormal鈥?copy, and this usually produces enough protein so there are no bleeding problems.

When a couple has children they pass on to each child one member of each pair of their chromosomes. For the sex chromosomes, a female passes on an X chromosome to all of her children, whereas a male can pass on either an X or a Y chromosome.

If a male with hemophilia has children with a woman who is not a carrier of a mutated gene for hemophilia, the following results are possible: a 50 percent risk for a son without hemophilia, and a 50 percent risk for a daughter who is a carrier. In order for them to have a daughter the X chromosome with the mutated Factor VIII or IX gene must be passed on from the father. These women are referred to as being 鈥渙bligate carriers." We know by the rules of inheritance that they are definitely carriers.

If a woman who is a carrier of a mutated gene for hemophilia has children with a man who does not have hemophilia, the following results are possible. A 25 percent risk for a son with hemophilia; a 25 percent risk for a son without hemophilia; a 25 percent risk for a daughter who is a carrier; and a 25 percent risk for a daughter who is not a carrier.


Picture of Pattern of Inheritance

Women who have family members with hemophilia may want to know if they have one copy of the mutated gene. DNA analysis is an extremely accurate method of testing to establish if a woman is a carrier of the hemophilia gene. DNA analysis begins with drawing a small amount of blood from a person in the woman鈥檚 family who has hemophilia. Analysis of the blood is done to identify the mutation that has occurred in the factor VIII or factor IX gene. In almost every family, the mutation is different. Once the mutation in the family is identified, any female who may be a carrier can be tested to see if she is a carrier.

Most female carriers have no health problems or symptoms related to carrying the hemophilia gene. These women are known as asymptomatic carriers. However, some female carriers have low factor levels that are associated with bleeding problems. These symptomatic carriers may suffer excessive menstrual bleeding, bruising, nosebleeds, and bleeding after surgery, dental work or childbirth. All women who are carriers should have a Factor VIII or IX baseline level evaluated.