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Thread: [help cant get out of it] Confusion related to coupled inherticance (genetics)

  1. #1 [help cant get out of it] Confusion related to coupled inherticance (genetics) 
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    Hello,

    I just cant seem to understand what they say:
    They have this fruitfly experiment in my book where they explain COUPLED inheritance:



    Now after this , they start explaining the "proof of crossing over". They try to explain that it happens with coupled genes:

    In the blue square they crossed a male AaBb with a female aabb, in the red square they crossed a female AaBb with a male aabb


    By this scheme they want to show that in the red square in the female AaBb there is CROSSING OVER in gametogenesis.
    After that they say that the male fruitfly doesnt do crossing over, while the female fruitfly DOES crossing over. Now here comes my question:

    If that were the case, why is it that in the 2nd image ( with the blue line & "?" ) there is NO crossing over? Because we only get AB & ab from a FEMALE AaBb, where are the crossed over gametes??!




    Thank you in advance!!


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  3. #2  
    Forum Professor Zwirko's Avatar
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    I can't read Dutch (or whatever). Does the diagram or the text in the book explain the difference between cis- and trans-linkage? That's what's probably going on the second image.


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  4. #3  
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    Does the diagram or the text in the book explain the difference between cis- and trans-linkage?
    Thank you for the answer first of all. No, they havent explained this, but why isnt there crossing over there? why is it showing only AB & ab . Theyre not showing Ab & aB. Isnt crossing over supposed to happen when a female fruitfly creates it gametes. Thats what my book says.
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  5. #4  
    Forum Professor Zwirko's Avatar
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    "Coupling" is when wild-type alleles are located on one chromosome and the mutant alleles are located on the other chromosome. Coupling is another word for cis-arrangement or cis-configuration. When each chromosome contains one wild-type and one mutant allele the linkage is referred to as "repulsion" and the alleles are said to be in the trans-arrangement or trans-configuration.


    The part of the diagram circled in blue with the arrow appears to be showing the mating of two members of the F1 generation: ABab x ABab. That is, two individuals of the type shown in the first circle are being mated in the box below.


    It's very confusing not understanding the language used in the diagrams, but I think this is what is going on.
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  6. #5  
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    I agree with Zwirko, that it is merely demonstrating the possible alleles that may be passed on by the heterozygous F1 mating.
    I can never know I'm right, but I can know that I'm wrong.
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