Homologous Structures Definition
The word homologous describes any sort of similarity in some ways. For example, if a pair of the chromosome have similar gene sequence and centromere location, they are called homologous chromosomes.
The homologous structures are exemplified in biology by the same anatomical composition or structural features of the body parts. According to evolutionary biology, the organisms having similarities indicate a common ancestor or the same developmental origin.
Homologous Structures Examples
i. Limbs: Humans and other animals contain similar bone parts in the upper limbs. The arms of humans and other animals contain the same set of bones, i.e. humerus, radius, and ulna. The arms of different animals are the example of homologous structures.
The forelimbs have the same anatomical structure but are used differently. They have the same embryonic origin, therefore, have a similar basic structure. The basic bone component of lower limbs is also similar among humans and other animals that composed of femur, tibia, and fibula.
ii. Vestigial Structures: Another example of homologous structures is vestigial structures that are remnants of the ancestral form. These structures alter their original function and remain in the body as remnants but they are used to study the evolutionary history of the species.
The common example of the remnant is the pelvis in snakes which is structurally similar to the pelvis of humans, dogs, and cats. The vestigial structures or remnants are also found in humans. For example- In the embryonic stage, the appearance of human tailbone show shreds of evidence that human and other mammals share a common ancestor.
Homologous Structures vs Analogous Structures
The structures having the same functions but differ in their anatomical structure are called analogous structures. The organisms having analogous structures represent dissimilar ancestors and do not show any evidence of common evolutionary lines.
They also may live in different locations but they use the body parts for similar functions. The example of analogous structures include wings of a bird, bat, and insect.
The wings of birds and bats perform the same function of flying but they differ in their composition, the anatomical features of these organisms are unrelated. Another example is the flippers of a whale and the fins of a fish.
The structures having similar functions but differ in their anatomy are called analogous structures whereas structures having the same anatomical features but different functions are known as homologous structures. Homologous structures show similar developmental patterns on the other hand analogous structures do not.