Question

Answer all three (a-c) questions about homology: (a) What is the difference between homology versus analogy? (b) Why is it important to make sure you use homologous characters rather than analogous characters to make phylogenetic trees? (c) Give examples from molecular and anatomical studies of the consequences of mistaken homology.

Answer 1

A.Homology

It is the classification of similar anatomical structures.Under this classification there seems to be evidential fact that the homologous structures have evolved from a recent common ancestor. If you consider a tree of life,the homologous organisms are more closely related to each other than the analogous counterparts.The homologous organisms seem to have undergone divergent evolution.

A widely sought example of homology is the tailbone in humans .Evidently our coccyx and tailbone have been vestigeal for so long but the cats and dogs still have their tails.

ANALOGY

When there is no clear indication that there has been or is a recent common ancestor between two organisms ,that is analogy. Considering the tree of life,in the case of analogy,the organisms may look similar and may even have similar functions ,still they are not related closely.Imagine two organisms living in similar climate and environment in 2 different parts of the world. It's the analogy that helps the organism to survive and thrive even in different adaptations.This is Convergent evolution.

B. Homologous structures show a similar embryonic origin whereas Analogous organs show similar function.Also, the homologous organisms have few sequence differences, whereas the analogous organisms have more sequence differences.While building a phylogenetic tree we aim to use shared traits in present day species so as to get an idea of their evolutionary history. Derived traits that are shared help us to build the phylogenetic tree. Traits can be gained and lost multiple times over the evolutionary history of a species. A species may have a derived trait, but then lose that trait (revert back to the ancestral form) over the course of evolution.

C. Mistaken homology leads to incongruities in methods and genes. It creates uncertainty regarding the true historical relationship of the organisms.