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In: Biology

an old biochemist compares 2 genes and says they are 80% homologous. what does homology mean?...

an old biochemist compares 2 genes and says they are 80% homologous. what does homology mean? do the sequences have to be identical to be homologous? what kind of scenarios would lead to 2 genes having 80% of their sites homologous and 20% of their sites non-homologous?

Solutions

Expert Solution

Homology

  • Homology refers to the study of similarity due to shared ancestry between a pair of structures
  • Structures or genes might have evolved from origin but they have different functions
  • A common example of homology is the hands of human being and wings of bat
  • It is caused due to the continuity of information
  • Sequence homology is the similarity between DNA, RNA or protein sequences based on shared ancestry

Criteria for being homologous

  • Two sequences are homologous if they are more than 30% identical over its entire length
  • Homologous genes can be similar in sequence
  • Similar sequences are not necessarily homologous

so the sequence need not be identical to be homologous.

Homologous genes are broadly divided into:

  • Orthologous
  • Paralogous

Orthologous genes:

  • These are homologous genes that diverged after evolution gives rise to different species by the process known as speciation.
  • It maintains a similar function to that of the ancestral gene that they evolved from.

Paralogous genes:

  • These are homologous genes that have diverged within one species.
  • These genes are new genes that hold new function and these genes arise during gene duplication where one copy of the gene receives a mutation that gives rise to a new gene with a new function
  • The function of these genes is often similar to the role of ancestral gene

Mutation can also lead to 2 genes having 80% of their sites homologous and 20% of their sites non-homologous.


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