What are the applications for each type?

There different types of FISH probes include: locus-specific probes, whole chromosome probes, and alphoid or centromeric repeat probes. 

1. Locus-specific probes target specific regions of a chromosome, helping researchers identify the chromosome consisting of a particular gene or determine the copy number of a gene. These probes are typically derived from genomic clones, which come in various sizes depending on the type of cloning vector used. Locus-specific probes are valuable instruments for detecting chromosomal abnormalities such as translocations, deletions and inversions, during both the metaphase and interphase stages of cell division. 
2. Whole chromosome probes consist of multiple smaller probes that bind to various locations along a chromosome's edge. They are complex DNA probes made from a single chromosome type that has been amplified using PCR and labeled to create a "paint" that illuminates the entire chromosome. When these paints are applied, they identify any structural or the number of abnormalities in chromosomes during metaphase. However, they are less effective for analyzing cells in interphase. These probes use a color-coded map (known as a spectral karyotype) or multicolor fish (M-FISH) to visualize these chromosomes; doctors use these methods to assess abnormalities in chromosomes. 
3. Alphoid or centromeric repeat probes are derived from short, repetitive sequences (which are repeated thousands of times) found in the center of each chromosome. They reveal the number of chromosomes present in an individual and can be combined with locus-specific probes to detect missing genes on a chromosome. Satellite DNA probes bind to the repeat sequences present at centromeres, producing bright fluorescent signals in both metaphase and interphase diploid cells. These probes are useful for detecting chromosomal abnormalities like trisomy, monosomy, and detecting various cancers (e.g. tumors and leukemia).