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Confused--phenotype with more than one gene from each parent

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Confused--phenotype with more than one gene from each parent

Postby airshipBN77 » Mon Dec 14, 2009 3:13 am

Okay, so we started on punnet squares and such in Biology. I understand how to to it when I only have one gene from each parent, but what about two? When I work it, I get an answer that (in my ignorance) doesn't really make much sense.

Say, for example, I have a heterozygous tall (Tt), purple-flowered (Pp) plant crossed with a short(tt), white-flowered (pp) plant. When I do the square, I get the possibilities of Pptt, Pppp, Tttt, and Ttpp. But this doesn't look right to me, because one of them does not have a specified flower color (Tttt), and another result does not have the height specified (Pppp). I am attempting to find the phenotype, and I have no idea what I would say with these results. I cannot ask my teacher, as we're on vacation. My textbook doesn't go any further than one gene from each parent. What am I doing wrong?
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Postby Darwin420 » Mon Dec 14, 2009 5:17 am

Seems like you are setting up your punnet square incorrectly.
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Postby jwalin » Mon Dec 14, 2009 11:53 am

gametes from Tt Pp are Tp and tP and TP and tp all 25% chances while ttpp give tp 100%
now cross the gametes from 1 with 2
it isn't what you do that matters but it is how you do it
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Re: Confused--phenotype with more than one gene from each parent

Postby JackBean » Wed Dec 16, 2009 12:25 pm

airshipBN77 wrote:Okay, so we started on punnet squares and such in Biology. I understand how to to it when I only have one gene from each parent, but what about two? When I work it, I get an answer that (in my ignorance) doesn't really make much sense.

Say, for example, I have a heterozygous tall (Tt), purple-flowered (Pp) plant crossed with a short(tt), white-flowered (pp) plant. When I do the square, I get the possibilities of Pptt, Pppp, Tttt, and Ttpp. But this doesn't look right to me, because one of them does not have a specified flower color (Tttt), and another result does not have the height specified (Pppp). I am attempting to find the phenotype, and I have no idea what I would say with these results. I cannot ask my teacher, as we're on vacation. My textbook doesn't go any further than one gene from each parent. What am I doing wrong?

Three answers and noone says, how to do it actually :roll: shame on you!

OK, you get one plant TtPp and the other ttpp. So, in first case, you can combine any of T or t and P or p, that is TP, Tp, tP, tp ;) In the other case, you can get only tp, so now just combine all cases from each, that is
TtPp, Ttpp, ttPp, ttpp ;)
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Re: Confused--phenotype with more than one gene from each parent

Postby vijeta » Fri Feb 12, 2010 10:01 am

When you set up a punnet square to find out the various outcomes, the allelic combination in the gametes should be properly mentioned.
Here TtPp the heterozygous parent forms 4 types of gametes- TP, Tp, tP and tp; whereas the other parent with genotype ttpp forms only one type of gamete- tp.
So now put the punnet cross with: TP, Tp, tP, tp x tp
You will get the following :
1 TtPp: 1Ttpp: 1 ttPp: 1 ttpp
which is nothing but 1 tall purple: 1 tall white: 1 short purple: 1 short white.

Now is that clear
?
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