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Fig. 4. An example of the presentation of data in a histogram format. The human chromosomes are end to end, p to q. The cDNA probe is for ceruloplasmin and is located on chromosome 3q25.
Genes that are single copy or low copy number require counting at least 100 metaphase spreads to determine the exact chromosomal location. Generally 10-15% of grains will be located at a specific band; 3-5 grains are observed per metaphase spread. Very rarely will one metaphase spread have both homologs labeled for a single copy gene. The data are represented graphically using a histogram of the chromosomes. An example of the type of data obtained is given in Fig. 4. Visual inspection of the data indicates the significant hybridizing site(s), but the data can also be analyzed statistically as illustrated by Morton et aV Genes with multiple copies at one site are much easier to analyze. Not only will both homologs have grains at the site, but also multiple grains often are found.
7 C. C. Morton, R. Taub, A. Diamond, M. A. Lane, G. M. Cooper, and P. Leder, Science 223, 173(1984).
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