Make Sense of How Hemophilia is Transmitted

Edited by Lor777, Eng, Nuance


It is common to find yourself still shouldering the responsibility for hemophilia, and looking for clues in your past behavior or medical history, especially if hemophilia does not run in your family. Hemophilia is not caused by stress, alcohol ingestion, medication taken during pregnancy, or bad behavior. It is an inherited trait, just like your hair, eye, and skin color. It can, also, appear spontaneously with no family history. It just happens, and no one and nothing is to blame. But, how was it transmitted? You may already know that usually only males inherit hemophilia. Why only males, and why only some males within a family?

To understand, you must learn a bit about genetics. Inherited traits are located in genes. Within the nucleus of every one of your 3 trillion body cells, there are 50,000 to 100,000 microscopic genes, grouped together on long pieces of DNA called chromosomes. Genes are the biochemical blueprints of the body; they produce hair color and skin color. These proteins determine how your organs will develop and function, how your bones will grow, what you will look like, and how well your blood will clot. When a gene that is supposed to contain the instructions for a key biological function does not work properly, it may lead to a genetic disorder such as hemophilia.

There are 46 chromosomes in each cell (except for the sperm and the ovum) arranged in 23 pairs. It is just in one pair of chromosomes that contains the gene with the incorrect directions for blood clotting; the gene that causes hemophilia. It is part of the chromosome pair that determines whether you'll be male or female. These chromosomes are called the "sex" chromosomes. Because the genes are found in the sex chromosomes, the appearance of hemophilia shows a definite pattern based on whether a boy or girl is created.

Here's How the Gene with Hemophilia Found Its Way into Your Child

  1. 1
    Unlike every cell in the body, aside from the egg or ovum, the sperm contains only 23 chromosomes. They are copies of half father's genetic make-up.
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  2. 2
    Egg or Ovum
    The egg also only contains 23 chromosomes. They are copies of half of the mother's genetic makeup.
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  3. 3
    When the sperm fertilizes the egg, the new cell contains 46 chromosomes. Half of them are from the father, and the other half are from the mother.
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  4. 4
    The egg contains an X chromosome.
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  5. 5
    The sperm can contain either an X or a Y chromosome.
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  6. 6
    Females XX
    As the egg always contains an X chromosome, a female is created when the sperm also contains the X chromosome. Every female is XX.
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  7. 7
    Males XY
    As the egg always contains an X chromosome, a male is created when the sperm contains a Y chromosome. All males are XY.
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Hemophilia 01.gif

So, a Girl (XX) will develop if the first sperm to reach and fertilize the egg contains an X. A boy (XY) will develop if the sperm contains a Y. Blood clotting capabilities are carried in the X chromosome. As females have two X chromosomes, even if one X is lacking the blood-clotting gene, the other is likely to have it. Because males only have one X, they are far more likely to develop hemophilia, as unlike with females, there's no backup X.

One Of The X Chromosomes Carries The Hemophilia Gene

If one of the X chromosomes carries the hemophilia gene then, the following will happen:


Girls will be a carrier - One X affected - one X not affected.

  1. 1
    Female carriers
    If one of her X chromosomes contains the hemophilia gene, the mother will be a carrier of hemophilia. In a carrier mother, half of all her X chromosomes have the defective gene. The other half will be unaffected, or normal. The mother probably doesn't have hemophilia because the other X has the correct blood clotting instructions. They produce enough factors in her bloodstream, but she can pass along an affected X to her child. If you are a mother who is a carrier: ##All of your children have a 50% chance of receiving the affected X chromosome.
    1. If you have a son, there is a 50% chance he will have hemophilia.
    2. If you have a daughter, there is a 50% chance she will be a carrier.
    3. It's like the flip of a coin: heads, it's a boy; tails, it's a girl. If it's a boy, flip again: heads, he has hemophilia; tails, he doesn't. Sometimes life with hemophilia seems that fickle, too.
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  2. 2
    Can a female have hemophilia
    In rare instances, a father with hemophilia and a carrier mother can produce a girl with hemophilia. In these rare instances, both X chromosomes are affected or one is affected and the other is missing or inactive.
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The male child will have hemophilia, because the Y chromosome is not affected, but the X chromosome is affected.

  1. 1
    Male babies
    When a male baby receives an affected X chromosome from his mother, he will have hemophilia. Why? As a male, he has an X and a Y chromosome, because he has no unaffected "backup" X that could produce the correct clotting instructions.
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  2. 2
    When this baby grows up to have children of his own, he will contribute either an X or a Y chromosome to create an embryo
    Each of his X chromosomes is affected, so:  
    1. All his daughters will be carriers of hemophilia.
    2. Each Y is normal, so his sons will be unaffected.
    3. If he has only sons, hemophilia will disappear from its direct ancestry.
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Tips Tricks & Warnings

  • When a child with hemophilia suddenly appears in the family tree, the mother may want to be tested to determine if she is a carrier. The results of being tested could influence family planning.
  • The decision to be tested should always be a personal one between you and your spouse.

If you have problems with any of the steps in this article, please ask a question for more help, or post in the comments section below.


Article Info

Categories : Blood Disorder & Issues

Recent edits by: Eng, Lor777

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