The Molecular Basis of Hereditary Diseases of the Kidney 
subunit of the G protein family. Since we have 
not been able to detect any large-scale deletions 
or rearrangements affecting any of the 22, we 
have begun to examine the sequence of these 
genes in detail and to look for mutations that may 
affect only one or two nucleotides. This work is 
supported by a grant from the National Institutes 
of Health. 
Our laboratory has been interested in the struc- 
ture of telomeres, the ends of chromosomes. We 
have shown that banks of repetitive sequence 
reminiscent of the sequence of human telomeres 
(TTAGGG) are also present at other sites within 
the human genome. One of the most interesting 
arrays of telomere-like sequence is embedded in 
the middle of the long arm of chromosome 2. 
Comparison of the chromosome banding pattern 
of humans with that of several closely related 
apes suggests that this region of the chromosome 
contains a point at which two ancestral ape chro- 
mosomes fused. Jaap IJdo, a Howard Hughes asso- 
ciate, has cloned this fusion point and shown that 
it consists of a head-to-head telomere-telomere 
fusion. 
In situ hybridization of a cloned DNA segment 
containing subtelomeric sequences to a human 
chromosome 2 (left). The fluorescent probe rec- 
ognizes the sequences at the tips of several 
chromosomes, including those of the long arm 
of chromosome 2 shown here. In addition, the 
probe recognizes another sequence (left 
arrow) that was buried in the middle of chro- 
mosome 2 when chromosomes of ancestral 
apes fused to create the human chromosome. 
(To this day the great apes have one more chro- 
mosome pair than humans.) The point of fu- 
sion is very close to a rare fragile site that was 
observed in the chromosome 2 used in this 
study. The chromosome on the right is shown 
with the hybridization signal removed so that 
the fragile site, which appears as a gap ( right 
arrow ), can be discerned. 
From If do, f.W., Baldini, A., Wells, R.A., 
Ward, D.C., and Reeders, S.T. 1992. Genomics 
12:835-835. 
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