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I am studying biology. While studying I have come across this paragraph:

Mutation is a phenomenon which results in 'alteration' of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism.In addition to recombination, mutation is another phenomenon that leads to 'variation' in DNA.

Can anyone explain the difference between using alteration and variation in this paragraph?

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alteration in the first sentence is used because the focus is on the modification of the DNA sequence. variation is used in the second sentence because the focus is not on the change itself but on the variety of the results. –  Jim Jan 24 at 0:01
    
@Jim I think you are stretching the point a bit here. They look more or less interchangeably used to me. If you swapped them around the paragraph would read virtually the same. However, in everyday use 'alteration' is a stronger word than 'variation'. The former means something more completely different, whilst variation usually means a less radical change. –  WS2 Jan 24 at 0:41
    
@WS2 - I guess we'll have to disagree. The point of sentence 1 is to say that mutation is a way to modify DNA. The point of sentence 2 is to say that because mutation modifies DNA it is another way in which many differences in DNA can be achieved. –  Jim Jan 24 at 1:26
    
@Jim You have now introduced a third alternative, 'modify'! I note you have helpfully edited the original, but it is still not well-written. It needs a 'thus' or a 'hence' at the start of the second sentence, I believe. I have tried to simplify it. 'Mutation results in alteration of DNA sequences... (Hence), in addition to recombination, mutation is another phenomenon that (varies) DNA'. Is there a difference between 'DNA sequences' and 'DNA'? One gets 'altered', the other 'varied'(by the process of mutation). Is that significant? –  WS2 Jan 24 at 7:04
    
@Jim If the distinction between 'DNA sequences' and plain 'DNA' is insignificant, could 'alter' and 'vary' be interchanged? Or is it the case that 'DNA sequences' are modified more radically than DNA itself'. If so then it seems using 'alter' for the first and 'vary' for the second makes good sense. –  WS2 Jan 24 at 7:13

3 Answers 3

up vote 5 down vote accepted

By alteration, they mean a change in the DNA of a single organism. An alteration to one organism makes its DNA different from other organisms in the same population. Variation is the range of differences in a population. If all the organisms in a population are very similar, variation is low. If some organisms in a population are quite different from others, variation is high. Over time, mutations increase variation. Natural selection reduces variation.

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+1 Variation plus natural selection equals evolution. –  andy256 Jan 24 at 0:38
2  
@kevin cline Indian cheetah's text, an online text from India's National Council of Education and Training, defines Variation to mean ". . . the degree by which progeny differ from their parents," which differs slightly from your definition. Your definition is more specific and consistent with a standard US biology text, Biology (Campbell/Reece), "differences between members of the same species." Here is a link to the NCERT text. textbook.s-anand.net/ncert/class-xii/biology/… I am not a fan of this text. –  Michael Owen Sartin Jan 24 at 1:00
    
@Micheal owen sartin, What you've commented is 100% true? The definition of Variation that is there in our book is exactly same as you've written in your comment. Can you please explain why they've given two definitions for mutation? According to kevin, variation is nothing but the measure of alteration (I think so). Am I correct? please help me. –  Akshay Nagraj Jan 25 at 10:53

It's important to note that they use the terms in quotation marks. That indicates that, regardless of the ordinary meaning such words may have, they intend a very specific meaning as likely described elsewhere in the text

Consider the following paraphrase from Furtama's Bender:

The only way to do that would be to make a "metaphorical" deal with the "devil." And by "devil", I mean Robot Devil. And by "metaphorical", I mean get your coat.

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I would say alteration denotes a generic form change (i.e. DNA could be less varied after alterations), the sentence just says it changes. Whereas variation is more specific about how the change manifests; the alteration caused by the mutation process leads to variation as opposed to uniformity (or whatever the antonym is).

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Alteration is not specifically generic as a form of change. The change is in the DNA. Variation is not more specific as a way of changing. Variation describes difference across a population. –  virmaior Jan 24 at 2:46
    
You did not understand my meaning. Simply said: alteration = change. Alteration is slightly less generic than change in that it may connote morphology or causality. You completely misinterpreted my explanation of variation, but it seems we agree on what it means. –  jiggunjer Jan 24 at 3:19

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