Genetics/Chi square help :(

[NubianPrincess]

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Im doing some of these chi sqaure problems, and the table is partially filled out so that I can tell i'm making a mistake somewhere. The questions says ..."in a dihybrid test cross, the following results were obtained......" and I was filling out the chi square table assuming that the expected ratio should be 9:3:3:1 and it occured to me that maybe my answer isnt coming out right because i'm assumning the wrong theorectical ratio.

I searched my texgt high and low and I cant find info on how to do a dihybrid test cross so that i can figure out what the theoretical ration should be. Can someone help me? 🙁 😕

 

[LoneCoyote]

Umm... I'm not sure if this will be helpful but I remembered some non- 9:3:3:1 dihybrid problems from my class. So I got out my notes and here's what my professor said.

9:7 ratio for mutations of genes in a single pathway if the mutant phenotypes are the same

9:3:4 ratio for mutations of genes in a single pathway if the mutant phenotypes are different (from recessive epistasis, where the mutation on the first protein in the sequence obliterates expression of a later acting protein)

So maybe if you have one of those two cases going on it could be different? Hope that's somewhat helpful. Good luck

🙂

 

[Adcadet]

maybe this will help:
http://www.biology.arizona.edu/mendelian_genetics/problem_sets/dihybrid_cross/dihybrid_cross.html

 

[NubianPrincess]

We havent done hw probs on modified rations yet (or maybe i'm just not up to them 🙁 )
Fortunately, that website kinda tells me what a dihybrid test cross is, so I should be able to figure out the answer from here. Thank you!