CoronationStreet
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So say if genotype Aa coded for green eyes why is its two letters why not just one?
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Zargabaath
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(Original post by CoronationStreet)
So say if genotype Aa coded for green eyes why is its two letters why not just one?
One for each allele, A represents a dominant one and a represents a recessive one.

You get one from each parent
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milkshakelover
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One is dominant and the other is the recessive allele.
That's how they exist.
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Asklepios
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(Original post by CoronationStreet)
So say if genotype Aa coded for green eyes why is its two letters why not just one?
Because humans, and generally most eukaryotes, are diploid. That is they carry two copies (or alleles) for each gene. So when we write the genotype for a specific gene, both alleles must be specified.
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TheConfusedMedic
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as above

and so you end up with 1/3 possibilities:
homozygous recessive - both recessive alleles
homozygous dominant - both dominant alleles
heterozygous - both alleles are different (1 recessive and 1 dominant)
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CoronationStreet
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(Original post by Zargabaath)
One for each allele, A represents a dominant one and a represents a recessive one.

You get one from each parent
A person who does not have cystic fibrosis could have CFCF genotype- why four letters (this is out of my text book_
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Gwilym101
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(Original post by CoronationStreet)
A person who does not have cystic fibrosis could have CFCF genotype- why four letters (this is out of my text book_
It is short hand for a Cystic Fibrosis (CF) allele. They've just use CF to clarify what the allele is for but its completely arbitrary.
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Asklepios
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(Original post by CoronationStreet)
A person who does not have cystic fibrosis could have CFCF genotype- why four letters (this is out of my text book_
I'm guessing in this case 'CF' means a normal non-mutant allele (I.e. Wild-type). So the person would have two of these. However this is quite strange notation and I've not seen it before. Normally you'd write CFTRWT/WT to denote a non-carrier. Here CFTR is the gene, and WT/WT shows both alleles are wild type. For a heterozygote carrier carrying a mutation, we would specify what mutation it is in the allele e.g. CFTRDelF508/WT means that one allele is normal and the other has a deletion of the amino acid phenylalanine at position 508.
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Zargabaath
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(Original post by CoronationStreet)
A person who does not have cystic fibrosis could have CFCF genotype- why four letters (this is out of my text book_
It probably refers to CF as one allele, i.e - the cystic fibrosis Dominant one
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