Homology is similarity due to shared ancestry. Homologous genes may have different functions and appearance due to evolution, but they originated from the same ancestor [1]. A more simple way of demonstrating this is through Figure 1, which illustrates how limbs share similar design across a wide variety of spices, but still varies both in appearance and even function. This same concept continues to apply at the molecular level with proteins!
Figure 1: Homology of limbs across species.
Homologs are most commonly categorized into two domains: orthologs and paralogs. Orthologs are differences between species while paralogs are genes that arise due to duplication events and exist within the same organism [2]. Figure 2 provides a clear visual demonstration of how all of these terms are related.
Figure 2: Visual representation of homolog, ortholog, and paralog relationships
ALK is a tyrosine kinase receptor protein, which is a common protein found across many different species. This allows for many different organisms to possibly model the protein of interest. The mouse has a similar homolog, conserved protein function, and permits for the disease phenotype of lung cancer to be easily modeled.
References
[1] https://ncse.ngo/what-homology [2] Jensen, R A. “Orthologs and paralogs - we need to get it right.” Genome biology vol. 2,8 (2001): INTERACTIONS1002. doi:10.1186/gb-2001-2-8-interactions1002