Dihybrid Cross Question??

[toothhornet88]

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So if a question asks to find ratios of the F2 generation and gives you the genotypes of the parents, does that mean I have to first find the ratios of the F1 generation and then use those ratios to find F2?

So if is TTRR x ttrr cross is done F1 will be all TtRr
and to get F2 you need to do a TtRr x TtRr cross to get 9:3:3:1 ratios right?

my question is: if the initial cross is different (say TtRR x ttRR) and you get more than one type of F1 genotype (ttRR, TtRR, TTRr, and ttRr in this case), do you have to make a seperate punnet square cross for each genotype to find the F2 generation?

Thanks in advance!!
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[lemoncurry]

yes, but in a cross of TtRR x ttRR, you would only get TtRR and ttRR as F1. Then for the F2, you would cross TtRR x TtRR, TtRR v ttRR, ttRR x ttRR. The ratio of offspring in each case would be 1:2:1, 1:1 and, er, 1. So no, you would not expect to see the 9:3:3:1 ratio of F2 with a P gen of TtRR x ttRR.

 

[toothhornet88]

yes, but in a cross of TtRR x ttRR, you would only get TtRR and ttRR as F1. Then for the F2, you would cross TtRR x TtRR, TtRR v ttRR, ttRR x ttRR. The ratio of offspring in each case would be 1:2:1, 1:1 and, er, 1. So no, you would not expect to see the 9:3:3:1 ratio of F2 with a P gen of TtRR x ttRR.

Got it thank you for doing them🙂 I appreciate it