i am reading a study related to my daughter's condition, ee, and i am having a hard time understanding one important part of it. i am taking a bio class (pre nursing student) and want to use this to write part of a paper on genetics.

http://www.jci.org/cgi/content/full/116/2/536

here's the part i'm having trouble with:

specifically the tendency to develop ee is tied to a single nucleotide polymorphism,rs2302009, 2,496 t--- >g . . . additionally, the frequency for genotype gg was significantly higher in patients with ee . . . from heterozygous parents, the allele g was preferentially transmitted to affected individuals compared with the alternative allele t .

i am trying to figure out if this means that people who don't have ee have thymine in that location but people with ee have guanine. or is this t and g alleles that the authors refer to are just letters they assigned to indicate the difference.

does genotype gg mean two guanines in place of one thymine, or does it mean they have two g alleles (one from each parent)?

i found this on wikipedia:

a single nucleotide polymorphism or snp (pronounced snip) is a dna sequence variation occurring when a single nucleotide - a, t, c, or g - in the genome (or other shared sequence) differs between members of a species (or between paired chromosomes in an individual). for example, two sequenced dna fragments from different individuals, aagccta to aagctta, contain a difference in a single nucleotide. in this case we say that there are two alleles : c and t. almost all common snps have only two alleles.

so i'm assuming it means a difference in nucleotides, right?

thanks so much for any insight you can give!

It is a difference in the nucleotide sequence. T's are subsitituted for G's or vice versa.

So Parent 1 has T allele and G allele (heterozygous) and parent 2 has the same make up. However the article states that G allele are preferentially passed on and the resulting offspring would have 2 G alleles (homozygous). Its not that 2xG's are in 1 T's place. This would cause a codon frame shift (potentially) and then you would get mutated proteins.

Thanks so much! :)