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Punnett Sq. Question

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Punnett Sq. Question

Postby bio1fall » Thu Oct 15, 2009 11:59 pm

Red-Green color-blindness is inherited as a sex-linked resessive. If a color blind woman mates with a man who has normal vision, what would be the expected phenotypes and genotypes of their children with reference to this character? What is the probability of having a color-blind child? A color blind son? A color blind daughter?

I dont understand how i would set up the punnett sq...

would it be like xxbb x xyBB
orrr... xxbb x xyBb???
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Postby JackBean » Fri Oct 16, 2009 1:04 am

If is it sex-linked, than it is on one of sex chromosomes, as it can have also woman, it must be on X ch.
So, you have like
xx (color blind woman must be homozygotic, as it is recesive) x XY
so basically you can get
xX and xY, so you will always get color blind boy and healthy girl (but which has one allel for color blindness, so half of their children will too etc.)

So, color blind child 50%
color blind son 100%
color blind daughter 0%
;) I hope so :)
http://www.biolib.cz/en/main/

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Postby JackBean » Fri Oct 16, 2009 1:20 am

I see, what's your problem, now.
Try this link :)
http://www.changbioscience.com/genetics/punnett.html
http://www.biolib.cz/en/main/

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Re: Re:

Postby bio1fall » Fri Oct 16, 2009 4:52 am

JackBean wrote:If is it sex-linked, than it is on one of sex chromosomes, as it can have also woman, it must be on X ch.
So, you have like
xx (color blind woman must be homozygotic, as it is recesive) x XY
so basically you can get
xX and xY, so you will always get color blind boy and healthy girl (but which has one allel for color blindness, so half of their children will too etc.)

So, color blind child 50%
color blind son 100%
color blind daughter 0%
;) I hope so :)


Okay Tnks i think you're right! I did some research and i think the punnett square should look like

XbXb x XBY

i think.. bc y chromosomes dont carry idk alleles????

am i right, or did i not explain it right... i need to know, cuz i need to show how i found it...
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Postby JackBean » Fri Oct 16, 2009 5:30 am

you are right, if you take Xb/XB as one nonbreakable thing! The gene is on X chromosome, so you are basically interested in whether there is or is not the X chromosome and which version, so you can basically take it only as xx x XY, OK?
http://www.biolib.cz/en/main/

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Re: Punnett Sq. Question

Postby joelle530599 » Tue Oct 27, 2009 4:39 pm

A cross breeder amateur is trying to get some crested canaries. He bought a couple of crested ones and coupled them. he obtained 21 eggs, among which 11 were crested and 4 were normal (without crest) , the others didnt hatch.
however, he changes the breeders but doesnt get any better results with other crested canaries couples: some eggs never hatch and the other give birth to crested canaries or to normal ones.
1) Are the crested canaries homozygous or heterozygous ? justify
i think it is heterozygous
2) Admitting that the crested character and the normal one are governed by only one couple of alleles, indicate whether there is dominance of an allele over the other or co dominance between the two alleles.
i didnt understand the question
3) write the genotypes of normal and crested canaries
Genotypes of normal: N//N
Genotypes of crested: C//n
4) Knowing that it is impossible to find crested canaries, if self crossed, that generate some exclusively crested canaries, search for a real explanation that some eggs never hatch ( the quarter on average)
i have no idea on this one
i need help in this problem as fast as possible
thxxx :)
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Postby JackBean » Wed Oct 28, 2009 3:55 am

Apparently, the homozygous crested stuff is lethal, so about 1/4 does not hatch, 2/4 are crested (heterozygotes) and 1/4 is back normal.
Just don't know, why at the genotype of crested you have C?
http://www.biolib.cz/en/main/

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Re: Punnett Sq. Question

Postby joelle530599 » Wed Oct 28, 2009 4:23 am

So as u answered, u mean that the crested canaries are heterozygous.
wat did u mean abt the genotype , they are wrong
do u have any idea about part 2 and 4 or can u ask anyone that can help
thx alot
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Postby JackBean » Wed Oct 28, 2009 8:28 am

OK, and now try to write it in English, OK? I'm not a decoding machine to read this :-/
http://www.biolib.cz/en/main/

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Re:

Postby jwalin » Wed Oct 28, 2009 12:39 pm

JackBean wrote:color blind daughter 0%
;) I hope so :)

just to add on the girl will be hetrozygous and a carrier
it isn't what you do that matters but it is how you do it
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Re:

Postby jwalin » Wed Oct 28, 2009 12:42 pm

JackBean wrote:Apparently, the homozygous crested stuff is lethal, so about 1/4 does not hatch, 2/4 are crested (heterozygotes) and 1/4 is back normal.

i think it's 11:4 i.e. 3:1 ratio
the concern about hatching or not hatching will be governed by another allele or gene.
it isn't what you do that matters but it is how you do it
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Postby jwalin » Wed Oct 28, 2009 12:43 pm

the crested ones are hetrozygous alright
it isn't what you do that matters but it is how you do it
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