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Well, here's what I did: P: Aa*Aa

F1: 1/4 AA, 1/2 Aa, 1/4 aa, SO the answer is 1/2, but out teacher did this: AA(1) Aa(2) aa(1) and she said we divide the number of filium for the phenotypes number and get 2/3. This is the probability. I don't get it.

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    $\begingroup$ why didn't you ask your teacher to explain when you didn't understand $\endgroup$ – WYSIWYG Mar 7 '15 at 10:45
  • $\begingroup$ You know in India it is very unlikely a student will ask a teacher about something (s)he does not understand. In many cases I have found out that the teachers themselves don't properly understand what they teach. The language is a huge barrier @WYSIWYG $\endgroup$ – One Face Mar 7 '15 at 13:38
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    $\begingroup$ @OneFace (a.k.a CRags :P) That is a problem with the education policy. We cannot do anything about it. We also cannot do a background search of a user before answering the question. Plus, you cannot generalize this for an entire country. $\endgroup$ – WYSIWYG Mar 7 '15 at 14:52
  • $\begingroup$ What is a "filium"? I would assume Latin for "children", but it isn't even correct Latin. $\endgroup$ – March Ho Mar 7 '15 at 18:19
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Okay so in your teachers answer there are four offsprings. . You used all offsprings when you made the division so 2/4 = 1/2.Your teachers 2/3 comes from the fact that 3 out of four is black, but only 2 out of that 3 black is heterozygote so 2/3 is good by this logic. I think that your teacher's logic faulty because you have to take into consideration all the offsprings. Basic genetics and Mendel's law tells us that crossing two heterozygotes with independent alleles result in a 3:1 ratio in phenotype separation in the next generation with 1:2:1 genotype separation -- that is what basically both of you have wrote. The fault is in the getting the probability - basic maths tells us that in an independent experiment, the probability variables have to sum up to one. In your teacher's logic this basic rule is not kept, because finding homozygous non-dark offspring would be one (there is only one non-dark filium and that one is homozygous). So by this logic all filium are non dark-homozygous, but then what about the others. I hope you see the problem with that logic.

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