Birthmarked and Genetics: A Rant

Ok, I reviewed this book already, now I need to rant about how bad this novel is at understanding middle school biology.

Inbreeding does not cause genetic disorders

I’m not saying that inbreeding is good. It’s not. It’s gross. Inbreeding does lead to an increase in a population’s genetic disorders, but it is not the cause. Let me explain.

No one’s genes are perfect, we all have genetic flaws. Even if you are genetically healthy, you still got some genetic flaws from your mom and some genetic flaws from your dad. If you are genetically healthy, your parents are genetically different enough that the flawed genes from your mom are covered by good genes from your dad. and the same with your mom’s good genes covering the flaws from your dad. So those genetic flaws just sit there not doing anything because they don’t have any friends to play with.

Don’t feel bad for that flawed gene! It could be the ectrodactyly gene for all you know!

Naturally, your close genetic relatives have much of the same genetic flaws that you do, because you know, you’re related. So having kids with, say your sister (gross) means the genetic flaws in your genes are more likely to find ‘friends’ in your sister’s genes, and they are going to go play in your kid’s genes. And your kid winds up with three fingers instead of ten.

So inbreeding does not directly cause genetic disorders, it just increases your likelihood of getting them.

There are genetic disorders OTHER than hemophilia

Birthmarked seams to work in a world where hemophilia is the only genetic disorder there is. With a plethora of horrable genetic deceases out there, you pick the one that is most easy to understand!

How hemophilia actually works

I asume you know what hemophilia is, if not, you’re already on the internet, look it up. Let’s not even get into hemophilia type B which is just a random mutation that pops up in otherwise healthy people. Let’s assume it is 100% inherited like in Birthmarked.

Hemophilia is a genetic disorder linked to the 23 set of chromosomes, yeah, the one that determines if you are born a boy or a girl. Hemophilia is caused by a mutation in the X chromosome of this pair.

Girls have a genetic advantage over boys when it comes to hemophilia. Since girls have XX chromasomes, they have something of a genetic fail safe for this condition. The non–affected X chromosone covers for the flawed one, so most girls with this condition never show any symptomes.

This condition is known as being a ‘carrier.’ Since boys have XY chromosomes they are kind of screwed. If they get the gene, they will be hemophiliacs. The inheritance for hemophilia looks like this:


Image from


I know what your thinking, what if the dad is the one with the gene. Well it would look like this:

Image from


Now it is possible for girls to be what’s known as “active carriers” of hemophilia, that means that they are genetically carriers, but instead of laying dormant, they exhibit some of the symptoms. What is very rair, is for girls to be full hemophiliacs because both of the X chromosones would have to be affected.

So lets think about this, if both the mother AND the father have the gene for hemophilia (like in Birthmarked) 50% of their sons will have hemophilia, 100% of the daughters will be carriers and 50% of the daughters will get two hemophilia genes and be a super awesome full hemophiliac.

Yeah, Stealing a handful of babies will save your culture!

We are told that everyone in the city, is at least a carrier of hemophilia, that means that outbreeding isn’t going to save them. At most, they can cut the odds of their daughters getting double hemophilia in half. but half of the sons will still be hemophiliacs, and that’s assuming everyone is outbreeding, which they are not!

They waited too long to address this problem. They could have simply open schools, teach the poor people their culture, and when the kids that you educated come of age, arrange marrages to insure the best possible genetic stock.

This culture is so authoritarian that they will rip babies from their mother’s arms, but they won’t arrange a few marriages?



“Hemophilia.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 20 June 2011,
“Inheritance Pattern.” Hemophilia Federation of America, Hemophilia Federation of America,

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