Orthology

In evolutionary biology, homology is 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 homologous. In genetics, homology is measured by comparing protein or DNA sequences, and genes that share a high sequence identity or similarity support the hypothesis that they share a common ancestor and are therefore homologous. 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. The word homologous derives from the ancient Greek ομολογειν, 'to agree'.
See more at Wikipedia.org...

(n.)
The right description of things.
  

Being homologous by descent. In other words, descendants from a common ancestor. An example is the MHC class II genes in different species all descended from a common ancestral class I gene.