Question

What are the homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?

Answer 1

Hint: It is the relationship between structures or DNA derived from the recent common ancestor. They may function differently from related organisms.

Complete answer
Homologous structures are a result of divergent evolution which explains that the same structures are developed along with different directions due to adaptations to different needs. It indicates that the homologous organs evolved from the common ancestor. Homology can be partial like new structures can develop through the combination of developmental pathways or parts of them.

Examples: The example includes the pattern of bones of forelimbs of whales, bats, Cheetah, and humans that share similarities in their structures but performs different functions according to their needs in these animals. Other examples include vertebrates’ hearts and in plants, the structure of thorn and tendrils of Bougainvillea and Cucurbita shows homology.
Homologous structures must always have a common ancestor. These structures are descended from the same developmental origin and serve as evidence of evolution. The similarities in proteins and genes that perform a given function among diverse organisms give evidence to common ancestry. In genetics, it is measured by comparing protein or DNA sequences of very different animals. There is a high similarity in Homologous gene sequences, supporting the hypothesis that they share a common ancestor.

Note: Anthropogenic action involves the excessive use of herbicides and pesticides that has resulted in the selection of resistant varieties of pests in very less time not in centuries.
Hybrid or mosaic structures can develop that exhibit partial homologies.