Back Testing for Birth Defects There are many types of tests that may be performed to determine whether a child has a genetic birth defect. Listed in the directory below are some, for which we have provided a brief overview. Chromosome Studies: Karyotype, Extended Banding, Fluorescence In Situ Hybridization (FISH), and Chromosomal Microarray Analysis Studies for Single Gene Defects: DNA (Direct and Indirect) Biochemical Genetic Testing