Context: discussing the children of a X(normal)Y Father and X(haemophilia)X(normal) mother.
Page 169 Genotype Check In Question d asks if there is a chance that a female child will have the phenotype haemophilia.
I said no as the daughter will either be X(normal)X(normal) so phenotype normal or X(normal)X(haemophilia) so as haemophilia is recessive the daughter will be a carrier but will have phenotype normal.
However the answers (Page 378) say there is some likelihood a female child will have haemophilia.
So am I missing something or is there a mistake in the answer section?
Thanks.
I would have answered the way you did. However, when I looked it up, I found out that some female carriers can have such low levels of the clotting factor that they are considered to have mild hemophilia. Who knew?
http://www.hemophiliafed.org/bleeding-disorders/can-women-have-bleeding-disorders/
As you know, X chromosome inactivation occurs in all the somatic cells of a female so that they won’t get a double dose of the X chromosome gene products. One would think that this process would be random, but sometimes it isn’t. There can be nonrandom inactivation of the maternally derived X chromosome. Skewing of the inactivation can result in having either more clotting factor or less clotting factor in a heterozygote. The Wikipedia article “Skewed X-inactivation” is helpful for understanding this. Below is an article that says that in some cases there may even be a heritable controlling factor that makes skewing more likely.
http://www.ncbi.nlm.nih.gov/pubmed/17342157
@BunnyBlue
Hmm, thanks, that’s really interesting. But it does contradict the information given both before and after the mini quiz in the Princeton Review book (which is obviously simplified to high school level) so I still think it may be an error in the textbook.
I was thinking the same thing. Hard to say whether the book intended that answer or not. Hope they don’t have that question on the real test.
So it’s wrong or right lol? Also, did you guys notice any other errors? Just wanna know cuz I just purchased the book like a few days ago.
@AniseedLollies I think you’re right. It’s probably a mistake in the answers cuz if you look at the bottom of page 169, it lists the probabilities of each child and for both females it says normal. So it’s probably a typo in the answers in part III.
@YoohooAddict
Thanks, I had another look at the page and all indications are it’s a typo.
I haven’t found any other errors in the book. A minor error in the Barron’s Literature Book on a crossword but nothing else in any prep book I’ve used. Let me know if you’ve found or find any mistakes!
@AniseedLollies I haven’t spotted any other ones either. Anyhow, I’ve read on threads from previous years that Princeton doesn’t cover some important topics that could possibly appear on the test i.e. plants & photosynthesis and anatomy of insects. I don’t know what to do then cuz I only have the Princeton book.
@YoohooAddict yikes! I hadn’t heard that! Are you sitting on June 4?
I have prepped exclusively from Princeton, but I have Barrons which I will start using this weekend. Hopefully I remember enough about plants from school…
@AniseedLollies Ya I’m taking it June 4th. No AP Bio or Bio Honors class prior to this so it’s gonna be tough 