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A sentence in my textbook is:

The possibility of female being haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life)

I know that haemophilia is an X-linked recessive disorder. Hence mother should be carrier and father must be affected for daughter to get affected. But I'm unable to understand what "unviable in the later stage of life" means.

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    $\begingroup$ I suggest that this question is more suited to SE Medical Sciences. $\endgroup$
    – David
    Mar 29 at 16:14
  • $\begingroup$ The Biology.SE community has agreed that questions that show little or no prior research effort are off-topic on this site unless you have shown your attempt at an answer. Please edit your question and tell us where you've looked for answers, what you do know about the topic, and where exactly you still have questions. ——— I mention this because if you had done the expected research you would have realized the premise of your question is incorrect. Note that under researched questions may be subject to down-voting and closure. Thanks! $\endgroup$
    – tyersome
    Mar 29 at 18:18
  • $\begingroup$ I suggest the exposition does not usefully touch on the Question title but still - and based solely on the actual wording - if "unviable in the later stage of life" came into it that would be down to aging weakening every system it came across. $\endgroup$ Mar 29 at 18:32
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Mortality.

The reason the most common examples of haemophilia in history occur among nobles is not because the nobles were a particularly sickly bunch of people. It is because they lived sufficiently pampered lives to actually become adults, and reproduce their haemophilia.

In the same era, a commoner or even a rich merchant family would not be very likely to keep a full haemophiliac male alive until marriageable age.

In our modern world, the almost-heroic level of medical care that is needed for a haemophiliac to live a normal life is much more common, and thus both carriers and active haemophiliacs tend to survive more often.

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I think what they mean is that those affected with haemophilia rarely survive to the adult life. This is less of a constraint for women, since a woman carrying only one recessive gene will not be affected by this disorder.

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    $\begingroup$ It must be a really old book though, as my dad's a haemophiliac and I'm 50 years old. He spent a lot of time in hospital as a kid and was told he's the oldest one with his level of factor to survive being born. $\endgroup$ Mar 29 at 16:43
  • $\begingroup$ @PeteKirkham impressive! It is probably also a genetics book - if it were on epidemiology, changing duration of survival with a condition would be something to discuss seriously ! $\endgroup$ Mar 29 at 17:02

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