Occasionally in cytogenetic studies, a genetic marker such as a large deletion or translocation (eg, 11p13 in aniridia) may be visible. Other markers used to identify the location of genes include blood groups (eg, as in Duffy blood group and Coppock cataract); restriction fragment length polymorphisms (RFLPs; eg, as in RP); microsatellites of variable number of tandem repeats (VNTRs); and most recently SNPs, as used in many GWAS. Cytogenetic tests are conducted on white blood cells, whereas the other genetic markers test DNA that is extracted most commonly from peripheral blood or saliva.
If a specific chromosomal structure is abnormal or even normally variant, its transmission through a family with a hereditary disease, as mapped by a pedigree, may support the assumption that the mutant gene and the variant chromosome are comigrating. Thus, the mutant gene is likely to be physically located on the variant chromosome—that is, the gene is a cytogenetic marker for the disease.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.