Specific Metaphase Chromosome Identification

The unambiguous identification of each chromosome
is prerequisite to defining structural
alterations associated with chromosomal imbalance.
With banding pattern analysis, chromosomal
resolution is limited by the size of the
recognizable bands and the relative similarity
of bands of different chromosomes. The smallest
chromosomal region detectable by light microscopy
in banded metaphase preparations is
about 5–10 million base pairs (5–10Mb). Such
a segment could harbor 10–50 genes.
The methods utilize individual differences of
DNA sequences of each chromosome and
special techniques to induce different color images
of each chromosome pair (”chromosome
painting”). The DNA of metaphase chromosomes
is first denatured (made singlestranded)
and then hybridized on a slide in situ
toDNA probes that make up a large collection of
DNA fragments from one particular chromosome.