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I was studying "Reproduction in Organism" as an interest of my own and there was a line

offspring produced through single parent are exact copies of their parent. Also, they are genetically identical.

So, in here, it says, "genetically identical" (I assume that identical here implies exactly same) but then the next line quite confused me.....

The term clone is used to describe such morphologically and genetically similar individuals.

Here, the term "genetically similar" is used.

So, clones (offspring produced through asexual reproduction- involvement of one parent) are "genetically exact" to their parents or genetically similar?

If "genetically exact", Then how is it possible since, there is 'No 100% efficient DNA Replication' that can be achieved?

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  • $\begingroup$ Aren’t you splitting hairs rather? I have no idea what book you are reading — you should always give a reference and preferably a link in questions — but the author of a book, like a lecturer in front of students is trying to communicate the essence of a concept, and if he hedged ever statement with disclaimers he’d never get his message across. Is it really important for what is being described and the distinction being made that there can be mistakes in DNA replication? $\endgroup$
    – David
    Commented May 23, 2020 at 22:25

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Biology is a lot messier than pure math, so if you insist on the same level of perfection and rigidity in definitions you are going to be very frustrated. You are correct that DNA replication is never 100% efficient, so "genetically similar" is probably a more literally accurate description of a clone. However "genetically similar" is a very vague term, which we might apply (depending on context) to two cells from the same individual, clones and parents, two siblings, a child and a parent, two unrelated members of the same species, or even two members of the same biological kingdom. It is sometimes useful to distinguish different levels of similarity, even if we acknowledge that the boundaries of our definitions are fuzzy and arbitrary. Saying two individuals are "gentically identical" is really a short-hand for "in the context of the phenomena we're looking at, genetic differences are so small as to be irrelevant"

If you look at the level of DNA base pairs, it's estimated the average number of base pair differences between two humans is about 20 million or 0.6% of the 3.2 billion base pairs in the human reference genome. Clearly that 0.6% difference can generate a lot of variation in readily observable traits. During development some cells in an individual will undergo somatic mutations, so even two cells from the same individual may not be literally genetically identical. For the most part (excluding catastrophes like cancer), these differences will be in only a handful of bases out of the 3.2 billion, and won't cause any observable difference in the two cells. The difference between a parent and their clone will mostly be these somatic mutations, probably with some additional mutations caused by the cloning process.

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