RFLP test for a partial gene
deletion in Thalassemia
The standard beta-globin
gene includes three exons (grey
boxes) separated by two introns (blue
boxes). One form of anemia, called thallasemia, is due to an
allele
(O) in which the third exon has been deleted and the resultant beta-globin
is non-functional. OO individuals are anemic:
AO heterozygotes have one copy of the standard allele, and
produce sufficient beta-globin, so that the AA and AO
phenotypes are similar. Thus, thallasemia is called a "recessive"
condition.
The beta-globin gene includes two restriction
sites (red lines) in the 5'
&
3' flanking regions: their nucleotide sequences are unaffected by the
deletion,
but their relative positions are closer in the O
deletion
allele. AA (standard) homozyogtes will thus have two
copies
of the full-length beta-globin gene RFLP
fragment, OO (thalassemia)
homozygotes will have two copies of the shorter RFLP fragment, and AO
(carrier) heterozygotes will have one copy of each fragment.
Note
that the molecular expression is co-dominant.
