copy of the same gene, all individuals will contain one region where their control sample is heterozygous but the mutant sample is homozygous - this region will contain the disease gene. Post-genomics techniques With the advent of modern laboratory techniques such as High-throughput sequencing and software capable of genome-wide analysis, sequence acquisition has become increasingly less expensive and time-consuming, thus providing significant benefits to science in the form of more efficient disease gene identification techniques. Identity by descent mapping Identity by descent (IBD) mapping generally uses single nucleotide polymorphism (SNP) arrays to survey known polymorphic sites throughout the genome of affected individuals and their parents and/or siblings, both affected and unaffected. While these SNPs probably do not cause the disease, they provide valuable insight into the makeup of the genomes in question. A region of the genome is considered identical by descent if contiguous SNPs share the same genotype. When comparing an affected individual to his/her affected sibling, all identical regions are recorded (ex. Shaded in red in above figure). Given that an affected sibling and an unaffected sibling do not have the same disease phenotype, their DNA must by definition be different (barring the presence of a genetic or environmental modifier). Thus, the IBD mapping results can be further supplemented by removing any regions that are identical in both affected individuals and unaffected siblings. This is then repeated for multiple families, thus generating a small, overlapping fragment, which theoretically contains the disease gene. Homozygosity/autozygosity mapping Homozygosity/Autozygosity mapping is a powerful technique, but is only valid when searching for a mutation segregating within a small, closed population. Such a small population, possibly created by the founder effect, will have a limited gene pool, and thus any inherited disease will probably be a result of two copies of the same mutation segregating on the same haplotype. Since affected individuals will probably be homozygous in the regions, looking at SNPs in a region is an adequate marker of regions of homozygosity and heterozygosity. Modern day SNP arrays are used to survey the genome and identify large regions of homozygosity. Homozygous blocks in the genomes of affected individuals can then be laid on top of each other, and the overlapping region should contain the disease gene. This analysis is often extended by analyzing autozygosity, an extension of homozygosity, in the genomes of affected individuals. This can be accomplished by plotting a cumulative LOD