 Medical genetics seeks to understand how genetic variation relates to human health and disease . When searching for an unknown gene that may be involved in a disease , researchers commonly use genetic linkage and genetic pedigree charts to find the location on the genome associated with the disease . At the population level , researchers take advantage of Mendelian randomization to look for locations in the genome that are associated with diseases , a method especially useful for multigenic traits not clearly defined by a single gene . Once a candidate gene is found , further research is often done on the corresponding gene – the orthologous gene – in model organisms . In addition to studying genetic diseases , the increased availability of genotyping methods has led to the field of pharmacogenetics : the study of how genotype can affect drug responses . 
