In biology,<unk> refers to the general and quite ancient observation of similarity of form seen in the biological world of animals or plants. It is the name given to the anatomical correspondences between different species that biologists and paleontologists have noted and studied for centuries.
More specifically, in evolutionary biology,<unk> has come to mean any similarity between characters that is due to their shared ancestry. There are examples in different branches of biology. Anatomical structures that perform the same function in different biological species and evolved from the same structure in some ancestor species are<unk> us. In genetics,<unk> can be observed in DNA sequences that code for proteins (genes) and in noncoding DNA. For protein coding genes, one can compare translated amino-acid sequences of different genes. Genes that share a high sequence identity or similarity support the hypothesis that they share a common ancestor and are therefore<unk> us.  Sequence<unk> may also indicate common function.<unk> us chromosomes are non-identical chromosomes that can pair (synapse) during meiosis, and are believed to share common ancestry.
The word<unk> us derives from the ancient Greek ομολογειν, 'to agree'.
Homology 
Character displacement
Dominance relationship
Expressivity
Quaternary structure
Special characters
Chemical affinity
Founder effect