Dihybrid Crosses

[SxyDentalDiva]

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Hey guys,

I'm fairly new to SDN & this like my 2nd post....so...

Practice Question: phenotypic ratio of Aaaa x Bbbb

I'm sure it's really simple but I can't figure it out. I know AaBb X AaBb is 9:3:3:1 but that's it.

If someone could help me out I'd really appreciate it. Thanks!

 

[SxyDentalDiva]

Corrrection...the question is asking for the F2 phenotypic ratio....

 

[Nateftw]

A little confused. You have Aaaa, which would mean that there are 4 chromosomes. Do you mean Aabb x aaBb? I assume so.

Break it up into two parts. Aa x aa, and bb x Bb.

Aa x aa gives 1/2 Aa and 1/2 aa

bbx Bb gives 1/2 Bb and 1/2 bb

therefore there will be 1/2*1/2 AaBb
1/2*1/2 Aabb
1/2*1/2 aaBb
1/2*1/2aabb

So in other words, there is a 1:1:1:1 phenotypic AND genotypic ratio

 

[SxyDentalDiva]

Thx Nate. That's the correct answer. I didn't understand how to work it out...but maybe I confused myself by writing it incorrectly.

 

[njohns24]

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[SxyDentalDiva]

Oh really? How was the test for you? When did you take it? Do you have any pointers?