Robertsonian Translocation what?

[FutureDoc4]

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Okay, I remember having this problem when I read it earlier in the year. The Robertsonian translocation for Downs Syndrome I have no problem with the concept of it (I think). Normal number of chromosomes, not related to age etc... However, I came across a question both earlier in the year and now.

Asking what is the probably of a mother's (who has a Robertsonian) translocation of having a child with Down syndrome fertilized by a normal sperm. I memorized the answer 1:3 (obviously memorization is not good for this boards/shelf etc).

Can anyone, in an easy to understaand way, say why its 1:3 (it's probably something VERY simple and I am just having a mental block with it)

 

[RapidReview]

Okay, I remember having this problem when I read it earlier in the year. The Robertsonian translocation for Downs Syndrome I have no problem with the concept of it (I think). Normal number of chromosomes, not related to age etc... However, I came across a question both earlier in the year and now.

Asking what is the probably of a mother's (who has a Robertsonian) translocation of having a child with Down syndrome fertilized by a normal sperm. I memorized the answer 1:3 (obviously memorization is not good for this boards/shelf etc).

Can anyone, in an easy to understaand way, say why its 1:3 (it's probably something VERY simple and I am just having a mental block with it)

i'm interested as well. why isn't it 1/2?

http://www.google.com/imgres?imgurl...sa=X&rls=en&tbs=isch:1&ei=Y7zZS_PDKYbINb-KuV4

 

[RapidReview]

i'm interested as well. why isn't it 1/2?

http://www.google.com/imgres?imgurl...sa=X&rls=en&tbs=isch:1&ei=Y7zZS_PDKYbINb-KuV4

FOUND IT! check out the first figure:

http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=iga&part=A2884&rendertype=figure&id=A2884

it's because 1/4 results in an non viable fetus, hence Down's is 1/3.

Thanks for asking, always good to refresh on my molecular genetics

 

[badasshairday]

edit: found the answer above.

 

[NRAI2001]

Okay, I remember having this problem when I read it earlier in the year. The Robertsonian translocation for Downs Syndrome I have no problem with the concept of it (I think). Normal number of chromosomes, not related to age etc... However, I came across a question both earlier in the year and now.

Asking what is the probably of a mother's (who has a Robertsonian) translocation of having a child with Down syndrome fertilized by a normal sperm. I memorized the answer 1:3 (obviously memorization is not good for this boards/shelf etc).

Can anyone, in an easy to understaand way, say why its 1:3 (it's probably something VERY simple and I am just having a mental block with it)

Hey,

I remember reading about it also and wondered the samething... how does it come out to 1/3. I think what it basically came down to was that the majority of the embryos with the translocation did not survive. So some how statistically it came out to 1/3.. but this 1/3 doesnt reflect inheritance patterns.

 

[RapidReview]

Hey,

I remember reading about it also and wondered the samething... how does it come out to 1/3. I think what it basically came down to was that the majority of the embryos with the translocation did not survive. So some how statistically it came out to 1/3.. but this 1/3 doesnt reflect inheritance patterns.

check out the 2nd link i posted above. it's bc 1/4 produces a nonviable fetus and the other 3 are viable, but only one of those will have downs.