Linkage analysis

Linkage analysis is very useful to determine the approximate location of an interesting gene, for example, one that is suspected to cause a disease or condition. To identify this gene, we can use markers or specific DNA sequences with known exact locations. For example, we can use microsatellites or SNP (single nucleotide polymorphism) as markers. By observing which allele variation is always present in the affected individual, we can then narrow down the approximate location of the gene.

We need to analyze many individuals in the family over several generations to identify the gene location because we need to find a specific allele that is always present in the affected individual and never present in the healthy individual. There are fewer genetic variations within a family because they are all genetically related.

This is why it is best to compare individuals within a close family rather than finding a healthy individual from an unrelated family. A healthy individual may have the same allele. However, because an individual comes from an unrelated family, that individual does not possess the disease gene. Therefore, we always need to compare within a close family.

When analyzing linkage analysis via gel electrophoresis, homozygous individuals have one band on the gel, while heterozygous individuals have two bands on the gel.