Question

- What are homologous structures?
A) Structures which have a common basic structure but perform different functions are called homologous structures.
B) Structures which do not have a common basic structure but perform different functions are called homologous structures.
C) Structures which have a common basic structure but perform the same functions are called homologous structures.
D) Structures which have a different structure but perform different functions are called homologous structures.

Answer 1

Hint:Homology means presence of similar structure, relation or position. By this, it is clear that homologous structures are structurally the same.

Complete Answer:
 Structural homology is the similarity in body structures occurring due to the presence of a common ancestral pair of structures or genes between organisms of different taxa. Structure of forelimbs in vertebrates is a common example of structural homology, similarities can be seen in the wings of bats and birds, the arms of primates, the front flippers of whales, forelegs of four-legged vertebrates like dogs, crocodiles can be seen. Similarities in all these structures are present due to the same ancestral tetrapod structure. According to evolutionary biology, homologous structures offer different purposes due to occurrence of descent modification passed on from a common ancestor. So, homologous structures are the ones which have a common basic structure but differ in functionality.
Therefore, the correct answer is- A. Structures which have a common basic structure but perform different functions are called homologous structures.

Additional information:Structures opposite to homologous structure are called analogous structures. Analogous structures have similar functions among organisms of different taxa that were absent in their most recent common ancestor. Rather, these structures evolved separately. The wings of insects and birds are examples of homologous structures, they evolved independently in different groups, and converged functionally to perform powered flight, they are called analogous.

Hence the correct answer is option ‘A’.

Note: Homologous structures are structurally the same but perform different functions. The evolution which leads to homology is called divergent evolution. In contrast to this, The evolution which leads to analogy is called convergent evolution.