Your opinion as to what homolgy is

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In summary, the term "homology" is typically used as a qualitative term to describe the relationship between two sequences that have a common ancestral origin. It can be further divided into two categories: paralogy and orthology. While statements like "sequence A is 95% homologous to sequence B" are common and can be considered correct, there is some ambiguity as to whether this refers to sequence identity or similarity. It is important to specify which is being measured. Additionally, it is generally preferred to use phrases such as "x% identical" or "x% similar under y scoring scheme" instead of referring to degrees of homology. However, in some cases, partial homology can be observed if only a certain portion of a
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farful
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In your opinion, do you think the word "homologous" is quantitative or qualitative?

That is, if I said "Sequence A is 95% homologous to sequence B!" would that be a correct or incorrect usage of the term?
 
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I think that the word homology is more of a qualitative term. Basically, if two sequences are homologous, they derived from a common ancestral sequence. You could split homology into two categories: paralogy and orthology. Orthologous genes are genes that play the same role in different organisms whereas paralogous genes are genes that derive from the a common ancestor but have diverged in function.

A statement like "sequence A is 95% homologous to sequence B" is commonly used and it could be considered correct. It can be somewhat ambiguous because there is a distinction between sequence identity (i.e. regions where sequence A and sequence B code for exactly the same amino acids) and sequence similarity (i.e. regions where sequence A and sequence B code for amino acids with the same chemical properties). Sequence homology is usually interpreted to mean the latter, though it would be better to specify whether one is looking at sequence similarity or sequence identity.
 
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Ygggdrasil said:
A statement like "sequence A is 95% homologous to sequence B" is commonly used and it could be considered correct. It can be somewhat ambiguous because there is a distinction between sequence identity (i.e. regions where sequence A and sequence B code for exactly the same amino acids) and sequence similarity (i.e. regions where sequence A and sequence B code for amino acids with the same chemical properties). Sequence homology is usually interpreted to mean the latter, though it would be better to specify whether one is looking at sequence similarity or sequence identity.

I think it is better to use phrases such as "The sequences are x% identical indicating that they are homologous", alternatively "x% similar under y scoring scheme". In undergraduate courses at my university the professors are very keen to stress that it is not sensible to talk about degrees of homology, and urge us to use this term as a strictly binary label: two entities are either homologous or not. They (the professors) also tend to apologize that some of the available literature is written without proper regard to this.

Because of gene shuffling it might make sense to talk about partial homology in the sense that z% of a sequence is shown to be significantly similar to some other sequence, suggesting that a subsequence of a sequence is homologous to some part of another sequence, while the rest of the sequence is not (or at least is more distantly related).
 

Related to Your opinion as to what homolgy is

What is homology and why is it important in science?

Homology is the similarity in characteristics between different species that is due to their common ancestry. It is important in science because it provides evidence for evolution and helps us understand the relationships between different organisms.

How is homology different from analogy?

Homology is based on shared ancestry, while analogy is based on similar functions. For example, the wings of birds and bats are homologous structures because they share a common ancestor, but the wings of birds and butterflies are analogous because they have different ancestors but serve a similar function.

What are some examples of homologous structures?

Some examples of homologous structures include the forelimbs of vertebrates, such as the arms of humans, the flippers of whales, and the wings of birds. These structures have similar bone structure, despite being used for different purposes in different species.

How is homology studied in genetics?

In genetics, homology is studied by comparing the DNA sequences of different organisms. If two species share a high percentage of similar DNA sequences, it is likely that they are closely related and have homologous structures.

Can homology be used to make predictions about evolutionary relationships?

Yes, homology can be used to make predictions about evolutionary relationships. By comparing homologous structures and DNA sequences, scientists can determine the degree of relatedness between different species and construct evolutionary trees to show their relationships.

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