Direct demonstration of a deletion

A partial deletion may cause an altered pattern
of a Southern blot. Two genes (!2 and !1) of !-
globin are presented (1). They are both located
on a 14.5 kb restriction fragment. If partial deletion
results in loss of a segment of, e.g., about
4.5 kb that is part of both the !2 and the !1
gene, a fragment of 10.0 instead of 14.5 kb will
result in this area (2). Three genotypes are
possible (3): two normal genes, !2 and !1, represented
by a 14.5 kb fragment; a normal DNA
segment (14.5 kb) and one with a deletion (10.0
kb); or a deletion in both gene segments (only
one fragment, of 10.0 kb). This can be demonstrated
directly in the Southern blot pattern
with a probe for the !1 gene (4).