Punnet Square Help Please

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princevisram
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Punnet Square Help Please

Post by princevisram » Thu Apr 08, 2010 10:24 am

Hello, I have two questions I could not get from my homework, I would be grateful if someone could guide me through them: (Book: Nelson Biology 11, Page: 167)


A recessive sex-linked allele (h) located on the X chromosome increases blood-clotting time, causing hemophilia.
(a) with the help of a punnet square, explain how a hemophilic offspring can be born to two normal products

I think if i do this question i can get the second one so please help.. Thanks :D

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JackBean
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Post by JackBean » Thu Apr 08, 2010 10:37 am

if you mean by two normal products "two healthy people", just imagine, what genotypes they have to have to be ill/healthy.
As it is recessive and X-linked, all the X chromosomes present must contain the ill allele (x), whereas healthy person must contain AT LEAST one healthy allele (X).
Thus, healthy women are XX or Xx and healthy man can be only XY. On the other hand, ill person must be xx or xY for woman and man, respectively.
Can you do the rest?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

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jwalin
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Post by jwalin » Fri Apr 09, 2010 9:32 am

lol
just to make an improvement in the representation
denote X normal as Xn and X haemophillic as Xh
it isn't what you do that matters but it is how you do it

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JackBean
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Post by JackBean » Sat Apr 10, 2010 6:49 pm

what's the difference between Xx and XnXh?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

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jwalin
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Post by jwalin » Sun Apr 11, 2010 11:48 am

no difference but it makes it easier when you write Xn Xh...
a little more better genetic reppresentation (as my teacher would have said)
but i personally think any can be used but prefer using Xn Xh
and as i said only an improvement in representation ;)


another idea
use XH and Xh instead of Xh and Xn
it isn't what you do that matters but it is how you do it

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JackBean
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Post by JackBean » Sun Apr 11, 2010 11:59 am

in what is it better genetic representation?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

princevisram
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Re: Punnet Square Help Please

Post by princevisram » Sun Apr 11, 2010 4:42 pm

Okay thanks but im still sorta confused.. what two sets of alleles would i cross in the punnet square? it would only be present in males right..?

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JackBean
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Re:

Post by JackBean » Sun Apr 11, 2010 4:45 pm

As I wrote:
JackBean wrote:Thus, healthy women are XX or Xx and healthy man can be only XY. On the other hand, ill person must be xx or xY for woman and man, respectively.


so you will have Xx vs. XY (the woman must be carrier, otherwise kid couldn't be affected), so all boys will be ill (xY) and all girls will be carriers as their mother
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

princevisram
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Re: Re:

Post by princevisram » Sun Apr 11, 2010 4:52 pm

JackBean wrote:As I wrote:
JackBean wrote:Thus, healthy women are XX or Xx and healthy man can be only XY. On the other hand, ill person must be xx or xY for woman and man, respectively.


so you will have Xx vs. XY (the woman must be carrier, otherwise kid couldn't be affected), so all boys will be ill (xY) and all girls will be carriers as their mother


.. X x
X XX Xx
Y XY xy


but thats not how i have it (see the chart above).. What am i doing wrong.. all the boys are not ending up ill (xY) as you said... Thanks btw for your help..

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JackBean
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Post by JackBean » Sun Apr 11, 2010 6:24 pm

not all of them, but the question was, how can two healthy people have ill child ;)
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

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