Can you tell me how is a karyotype helpful to persons with possible genetic problems?

A karyotype reveals the structure and number of chromosomes (bundles of genetic material) in a person's cells. If the structure or number of chromosomes is abnormal, this can cause health problems. For example, in the most common form of Down syndrome, there is an extra copy of chromosome 21 in each cell. For more info see: https://www.genome.gov/genetics-glossary/Karyotype