What does the term 'linkage' refer to in genetics?

In genetics, the term 'linkage' refers specifically to genes that are found on the same chromosome. When genes are on the same chromosome, they tend to be inherited together during the process of meiosis due to their physical proximity. This proximity can reduce the likelihood of recombination, or crossing over, occurring between them, leading to a higher chance that they will be passed down as a unit to the next generation.

Understanding this concept is crucial because it contrasts with the behavior of genes on separate chromosomes or genes that are located far apart on the same chromosome, which may assort independently during meiosis, increasing the chance that they will not be inherited together. The idea of genes that are always inherited together is a simplification; while linked genes do tend to be inherited together more frequently, they are not guaranteed to be so, as recombination can occur between them under certain circumstances. Thus, the term 'linkage' effectively captures the relationship of genes residing on the same chromosome.