This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.
What Is Homology?
When comparing and contrasting certain traits in organisms, biologists often look at similarities in structure, function, and evolutionary ancestry. Features of animals that have similar structure are classified as homologous if they have a common evolutionary origin [1]. This is true even if they have different functions in different animals. A classic example of homologous structures is that of the wing of a bat and the arm of a human [1]. Both structures can be seen above in Figure 1. Both have similar internal bone structure, and as mammals, the evolutionary origin is clearly similar. However, both structures have completely different functions. The wing of a bat is utilized for flying, whereas the arm of a person is used to carry items and to perform other tasks. Similarly, the leg of a dog, wing of a bird, and fin of a whale are also homologous to the human arm. Such structures are said to have diverged over time, indicating that at one time, they may have had the same function in the common ancestral organism [1].
In genetics, homology is measured by comparing protein or DNA sequences, and homologous genes share a high sequence identity or similarity, supporting the hypothesis that they share a common ancestor. Sequence homology may also indicate common function. Homologous chromosomes are non-identical chromosomes that can pair (synapse) during meiosis, and are believed to share common ancestry [2].
In genetics, homology is measured by comparing protein or DNA sequences, and homologous genes share a high sequence identity or similarity, supporting the hypothesis that they share a common ancestor. Sequence homology may also indicate common function. Homologous chromosomes are non-identical chromosomes that can pair (synapse) during meiosis, and are believed to share common ancestry [2].