Final answer:
A bright red signal in CGH analysis along chromosome 3's short arm indicates more red-labeled reference DNA hybridization than green-labeled test DNA. This suggests a deletion in the test DNA at this region compared to the reference DNA, pointing to a possible genetic abnormality.
Step-by-step explanation:
CGH, or Comparative Genomic Hybridization, involves the hybridization of differentially labeled genomic DNA (test sample and reference sample) onto a normal chromosome spread. In this instance, the test DNA was labeled with Cy3 (green) and the reference DNA with Cy5 (red). A bright red signal along the short arm of chromosome 3 indicates that in this region, there have been more red-labeled reference DNA hybridized compared to the green-labeled test DNA. This typically suggests a deletion in the test DNA when compared to the reference DNA, as the lack of green signal from the test DNA means there is less or no DNA from the test sample to hybridize in this region, resulting in a predominance of red fluorescence.
It's essential to interpret the CGH results in the context of the fluorescence intensity. A purely green or red spot means that only one of the DNA samples hybridized at that spot, while a yellow spot would indicate hybridization by both samples. Therefore, the appearance of a bright red signal along the short arm of chromosome 3 is indicative of test DNA having less genetic material in that region compared to the reference, suggesting a possible genetic abnormality within the test sample.