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    Can't really find a thread for this exam.. How is everyone feeling about it? any thoughts on what might come up? Any tips on getting over the A* boundary?
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    Also I have a past paper question which seems to be literally impossible to solve.. the questions from june 2014 question 4b (iii). you've been told that in chickens are XX male and XY female. the allele f is recessive and for rapid feather production. Allele F is dominant to f and is for slow feather production. This is the question..

    A cross between two chickens produced four offspring. Two of these were males withrapid feather production and two were females with slow feather production. Give thegenotypes of the parents.

    The answer in the mark scheme gives XfXF and XfY.

    after doing a punnet square this definitely isn't right.. Any ideas??
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    Well because how how sex-linked characteristics work the two males will have F and will get the F allele from their mother and the females who were XfXf will have got one of their alleles from their father and the other from their mother. This means that the mother has to be heterozygous as the males have F and the daughters are both f. The father has to be f because the daughters are homozygous. Hope this helps as i dont think ive explained it well it just makes sense in my head if you know what i mean
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    yeah I got it but why doesn't it work in a punnet square? Because you should still be able to do sex linked characteristics like that right?
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    no wait your answer wouldn't work because they said in the question that in chickens females are XY and males are XX, so then in that case the male would get one allele from the mother and one allele from the father, and as the males are homozygous recessive the mother would have to be XfY.. then the father would be XfXF in order to get a female offspring which is XFY.. and that also wouldn't work because it would result in one of the two male offsprings being heterozygous which would mean the dominant allele F would show in the phenotype and it would have slow, not rapid feather production..
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    The offspring must be

    XFY, XFY both female
    XfXf, XfXf both male

    I think the exam board modelled the answer on the chromosomes being XX female and XY male and forgot that they changed it for chickens...
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    (Original post by RosieHA)
    The offspring must be

    XFY, XFY both female
    XfXf, XfXf both male

    I think the exam board modelled the answer on the chromosomes being XX female and XY male and forgot that they changed it for chickens...
    No, it's because the actual offspring they had does not replicate the exact punnet square- the punnet square shows possible options. So basically the parents just produced 2 offspring with 1 genotype and 2 with the another, and 0 with the other two options you would see in the punnet square.
 
 
 
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