Punnett squares

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littlepeach0918
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Punnett squares

Post by littlepeach0918 » Wed Jul 05, 2006 4:29 am

In guinea pigs, black fur is controlled by a dominant gene, B. White fur is due to the recessive, b. Draw two punnet squares and fill in the information to show the results of (a) crossing a black male that is homozygous dominant with a white female that is homozygous recessive. And (b) a male and female from the first generation of offspring to make a second generation. Give the phenotype and genotype ratios for the offspring in each generation.


I don't really know where to begin with this problem so I just wrote down the info. and my squares and after that I froze, so please help

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mith
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Post by mith » Wed Jul 05, 2006 4:58 am

use the forum search, been discussed many many times before

http://biology-online.org/biology-forum/search.php
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sgliverpool01
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here you go!!!

Post by sgliverpool01 » Wed Jul 05, 2006 2:57 pm

crossing BB with bb will give an F1 generation of Bb

then cross two Bb to give: BB, Bb, Bb and bb
this is the F2 generation

You can work out the ratios easy!! :D

good luck

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sunnygirl
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Post by sunnygirl » Tue Aug 01, 2006 12:38 am

Im having a similar problem, im doing a Punnett dihybrid cross...
the red color (R) is dominant over white (r) and being tall (T) is dominant over short (t)

Rrtt x rrTt
i did the cross but i dont understand how to find the 4 possible genotypes and phenotypes from the cross.... any suggestions?
*AGAPE*

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James
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Post by James » Tue Aug 01, 2006 1:15 am

You need to find a method that can be used for all dihybrid crosses, something like:

Parent phenotypes
Parent genotypes
Gametes
Punnett square
F1 genotypes
F1 phenotypes
Ratios

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sunnygirl
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Post by sunnygirl » Tue Aug 01, 2006 1:26 am

ok then i think i did it totally wrong....... OoPpppsss
Now let me try that square again and see what i come up with
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sdekivit
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Post by sdekivit » Tue Aug 01, 2006 1:56 pm

sunnygirl wrote:Im having a similar problem, im doing a Punnett dihybrid cross...
the red color (R) is dominant over white (r) and being tall (T) is dominant over short (t)

Rrtt (1) x rrTt (2)
i did the cross but i dont understand how to find the 4 possible genotypes and phenotypes from the cross.... any suggestions?


use the gametes Rt,Rt,rt and rt for individual 1 and the gametes rT,rt,rT and rt for individual 2 and draw the square.

Notice that this is a time consuming work that has to be done. You can see easily now from the gametes the genotypes RrTt, Rrtt, rrTt and rrtt will occur

--> phenotypes: red/tall, red/short, white/tall and white/short

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sunnygirl
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Post by sunnygirl » Tue Aug 01, 2006 3:58 pm

ok thanks that hepl me alot! i begining to understand how to do it now, thanks ;)
*AGAPE*

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