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Mendelian's - epitasis 9:3:4 , biology

  1. Oct 19, 2015 #1
    After I have done counting the corn and the result 267 yellow , 97 white , 144 purple
    ratio 9:3:4 respectively . Recessive - Epitasis ?
    I have no idea create a inheritance cross and the biochemical influence by genes interaction from
    this phenomena
     
  2. jcsd
  3. Oct 19, 2015 #2

    epenguin

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    That by itself is not a phenomenon. If I told you the number of books of different colours on my shelves would that be a phenomenon?

    You have to state what this corn your counted has come out of. Some cross? The total descendance after n=? generations from two ancestors? Something else?
     
  4. Oct 20, 2015 #3
    This is the dihybrid cross where the parents are purple ( rrCC ) x white ( RRcc)
    F1 generation all RrCc(yellow ).The result is F2 generation in the ratio 9:3:4 . (Yellow:white:purple)
    What kind of gene interaction is this and how should I explain it?
     
  5. Oct 21, 2015 #4

    epenguin

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    I can't say I ever met this sort of situation before, but I found a, repeat a, possible solution so it Is not a question of expertise, just thinking.

    9 + 3 + 4 = 16, convenient. Take one gene and the three genotypes are in ratio 1/4: 2/4: 1/4 or 4/16: 8/16: 4/16 . You can probably see where your 4/16 purples are coming from. I wrote out a tree - top layer

    RR. Rr. rr
    4. 8. 4


    Then on next layer wrote the three genotypes that come under each of those in F2 with their expected frequencies in sixteenths.

    Excluding the purples I looked for what combinations of c/C's do I see 3 of? There seems to be more than one answer, I don't know if there is other information to distinguish these, but getting that far is the main thing.
     
    Last edited: Oct 21, 2015
  6. Oct 29, 2015 #5

    epenguin

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    OP not come back, not recommending self for any future help but I think it is a shame to leave questions unanswered like this when the answer is so simple yet maybe not at first sight obvious.

    Point is a bit of familiarity helps a lot with genetics - geneticists can look at quite complicated data and reel you off the explanation just like that while you have to work it out more slowly on paper, in fact I wrote myself out the genotype frequencies as mentioned in #4.

    But then I see, just in your head, what can explain 3/16 whites? Simples - first the data indicated that RR makes purple independent of the C locus, but presence of two R necessary for it. That is 4/16 cases, now of the 12 left 3 are white, that's just the expected 1/4 of homozygous for C, when you have 1:2:1 i.e. 3:6:3 of cc:Cc:CC. White recessive.
     
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