Confused with punnet squares - me and teacher

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jnicholas
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Confused with punnet squares - me and teacher

Post by jnicholas » Mon Feb 09, 2009 10:22 am

Hi All, a homework question I have researched and tried and I have just about rubbed through the page. The teacher did not explain how it all works. I have done basic punnet squares but this is trickier so here it is...

The allele for tall pea plants (T) is dominant over the allele for short pea plants (t) The allele for purple pea plant flowers (P) is dominant over the allele for white pea plant flowers (p)

Complete Punnet Square for cross between male short pea plant with purple flowers (genotype ttPP) and a female pea plant with white flowers (genotype Ttpp)

I am having trouble assigning the letters to the correct columns /rows the table is 4x4 with Male gametes across the top and Female down the side.

Help is much appreciated... Thanks

Think that is all

seasaba22
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Re: Confused with punnet squares - me and teacher

Post by seasaba22 » Mon Feb 09, 2009 3:32 pm

Do it this way -
____Tp | Tp | tp | tp
tP |
tP |
tP |
tP |

Your results should be (going by columns): (highlight to see)
TtPp, TtPp, TtPp, TtPp; TtPp, TtPp, TtPp, TtPp; ttPp, ttPp, ttPp, ttPp; ttPp, ttPp, ttPp, ttPp
The possible outcomes are TtPp as tall/purple, ttPp as short/purple

jnicholas
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Re: Confused with punnet squares - me and teacher

Post by jnicholas » Mon Feb 09, 2009 8:07 pm

so how do you work out the genotype and phenotype ratios?

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mith
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Post by mith » Mon Feb 09, 2009 10:52 pm

The problem is pretty much worked out if you have the square setup. If you don't know how the square works, now's the time to review.
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Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
~Niebuhr

GeGnome
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Re: Confused with punnet squares - me and teacher

Post by GeGnome » Thu Feb 12, 2009 7:59 am

jnicholas wrote:so how do you work out the genotype and phenotype ratios?


First bit of advice: switch seasaba's format if you want males on top and females on bottom.

As for genotype and phenotype ratios, let me demonstrate with a 2x2 punnet square:

T = Tall (dominant)
t = short

Both male and female are Tt
___ T | t
----------------
T| TT | Tt
----------------
t | Tt | tt
----------------
Genotype ratio = 1/4 TT; 1/2 Tt; 1/4 tt (This includes everything and it's out of four because 2 x 2 = 4)
Phenotype ration = 3/4 Tall; 1/4 Short (Phenotype is only the traits that are expressed.)

Extrapolate this information to 4x4 punnet square. 4x4 = 16.

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