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    F = Dominant, no cystic fibrosis.
    f = Recessive, no cystic fibrosis.

    I understand that if someone is 'ff', the recessive allele is expressed.
    1 - Does this mean that their phenotype can be described as 'cystic fibrosis'?
    2 - Where does genotype come into play here?
    3 - The above makes them homozygous; if they have 'FF' and thus don't carry it at all, are they also considered homozygous?
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    1. Yes if the genetic diagram is ff then the phenotype is to be stated as having cystic fibrosis
    2. The genotype is the 'ff' representation of the gene's inherited
    3.Yes it is homozygous, as the alleles are the same in this version of the inheritance
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    1) There phenotype would be the recessive allele therefore they would inherit cystic fibrosis from the parent.
    2) The genotype would be the mutation of the gene represented by the 'ff'
    3) Finally homo is two of the same alleles so yes, FF would be homozygous however the children with Ff or fF are heterozygous, and the ff child would be homozygous also
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    Homozygous for a gene just means - both your copies are the same. In Ff then one copy is defective and one is correct, which is heterozygous because you've got two different types (allele) of the gene. FF and ff are both homozygous because you've got two copies of the same allele.

    Phenotype is what is expressed and genotype is what your actual genetic material says. Sometimes these are the same. FF and ff would have the same genotype and phenotype - no cystic fibrosis and cystic fibrosis respectively! But it's important to distinguish genotype and phenotype when you've got somebody who is Ff. Their phenotype is no cystic fibrosis, but their genotype is that they are a carrier. Obviously there's a big difference between somebody who is 'no cystic fibrosis' but actually genotypically Ff versus somebody who is genotypically FF and has nothing to worry about.

    Hope that makes sense of it.
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    (Original post by DoubleDoors)
    F = Dominant, no cystic fibrosis.
    f = Recessive, no cystic fibrosis.

    I understand that if someone is 'ff', the recessive allele is expressed.
    1 - Does this mean that their phenotype can be described as 'cystic fibrosis'?
    2 - Where does genotype come into play here?
    3 - The above makes them homozygous; if they have 'FF' and thus don't carry it at all, are they also considered homozygous?
    As the others have said, both are considered homozygous. The distinction is that FF would be considered 'dominant homozygous' whilst the ff genotype would be considered 'recessive homozygous'.
 
 
 
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