General Genetics/Diseases and Genes
The understanding of genetics among the health sciences community has exploded with the advent of next generation sequencing allowing geneticists to associate regions of DNA with genetic diseases. Genetic diseases and disorders can be caused by aneuploidy, mutated genes, or areas outside the gene that have been mutated to up or downregulate the function of a gene.
Disease geneticists wanting to study can start their research by selecting a known disease, gather a population of both affected and unaffected individuals, and sequence their genomes to see regions of similarity and difference. This process can be assisted by functional genomicists who analyze particular regions of the genome, ideally a gene, and work towards understanding its function. For example, if a functional genomicist uncovered a gene that was crucial in the regulation of insulin production, a geneticist attempting to understand the underlying causes of diabetes would want to know if this gene was of a similar sequence in the genome of affected individuals. For animal genetics, you could mate two affected individuals and sequence the genomes of the affected progeny. Similarity in the area of interest indicates that that region of DNA, and that sequence, are responsible for the genetic disorder.