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According to Genomes

PCR is

A technique that results in exponential amplification of a selected region of a DNA molecule [in test tube].

DNA cloning is

Insertion of a fragment of DNA into a cloning vector, and subsequent propagation of the recombinant DNA molecule in a host organism.

While, Molecular Biology of the Cell, Sixth Edition says in a summary:

DNA cloning (through the use of either cloning vectors or the polymerase chain reaction) in which portion of a genome (often an individual gene) is purified away from the remainder of the genome by repeatedly copying to generate many billions of identical molecules.

Here DNA cloning has been used to mean DNA replication in general.

Question: Which author's view is correct, or at least provides the most accepted definitions?

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Short answer

The Oxford English Dictionary is quite clear on this. For the verb clone there are two meanings:

Biology To propagate (an organism or cell) as a clone.

Molecular Biology To make copies of (a DNA sequence or gene).

The latter definition clearly encompasses PCR.

History lesson

Most of the information below is taken from the Oxford English Dictionary.

The term clone has a long history, first as a noun and more recently as a verb. The evolution of the meaning and use of the word suggests that we shouldn't be too precious about this.

When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean—neither more nor less.” “The question is,” said Alice, “whether you can make words mean so many different things.” “The question is,” said Humpty Dumpty, “which is to be master—that’s all.

The word is based on a Greek word for twig and was originally used as a noun in the form clon.

1903 H. J. Webber in Science 16 Oct. 502/2 Clons..are groups of plants that are propagated by the use of any form of vegetative parts.

It soon gained the final e.

1905 C. L. Pollard in Science 21 July 88/1 I therefore suggest clone (plural clones) as the correct form of the word.

By 1930 it had become a verb...

1930 Jrnl. Ecol. 18 357 This is probably a record for the number of ‘individuals’ obtained at one time by cloning a herbaceous plant

...and, presumably because bacteria were considered to be plants at that time, it was used in microbiology too.

1929 Bibliographia Genetica 5 234 In Bacillus coli communis...a biotype was also found having lower motility than the remainder of the clone from which it came.

By the early 1960s it was extended to animals, probably as a direct result of Gurdon's experiments with Xenopus

1963 J. B. S. Haldane in G. Wolstenholme Man & his Future 352 Perhaps the first step will be the production of a clone from a single fertilized egg, as in Brave New World.

And finally the meaning was extended to encompass DNA molecules, thus molecular cloning.

1974 Proc. National Acad. Sci. U.S.A. 71 3459/1 ColE1 has been shown to serve as an effective molecular vehicle for cloning and amplifying specific regions of unrelated DNA.

(Extra points if you have read this far AND you know what ColE1 is.)

This final quotation seems to me to show that the confusion over what molecular biologists mean by cloning arose very early. If cloning means “to make copies of” then why is the word amplifying there? From the outset I think that molecular cloning carried the sense of purifying (by cutting and ligating). Or that's what I thought when I did it for the first time in 1980.

Update

Despite my reliance on dictionary definitions above, and prompted by Tyto alba's discovery of a contradictory definition in a different OUP publication (see comment) here's what I really think:

Anyone who has ever obtained a bacterial colony containing a plasmid with the inserted fragment that they wanted announced "I have cloned the gene!" and meant that they had made a recombinant plasmid AND got it into cells. On the other hand, if they started with a PCR amplification then ran a gel to check before ligating and saw a fragment of the expected size they did not say "I have cloned the gene!" And finally, the successful cloner, when streaking out their transformant colony, will rarely have referred to this step as cloning.

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  • $\begingroup$ I found in 'A dictionary of genetics' (published by Oxford again) say it means creating genetically identical copies of recombinant cells, excluding the in vitro part (pg-182)?! Should OED be considered more precise when we are looking at words as this? $\endgroup$ – Tyto alba May 9 '17 at 17:56
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Short answer
All of your sources are correct as they are not mutually exclusive. PCR is used to isolate and amplify DNA to yield small quantities of pure target product. Gene cloning can subsequently be applied to scale the production of the fragment up. PCR thus can be part of the DNA cloning process.

Background
Cloning in general simply means duplicating. Cloning in Biology refers to

[Making] an exact copy of an animal or plant created in a laboratory from the animal’s or plant’s DNA

source: McMillan Dictionary

Gene cloning, as far as I understand refers specifically to the isolation of one single gene and inserting it into cells to amplify it:

The production of a lineage of cells all of which contain one kind of DNA fragment of interest derived from a population of many kinds of DNA fragments.

source: Northwestern University

PCR is a technique to amplify a specific strand of DNA that can be used to subsequently clone DNA into host cells (source: New England Biolabs). The cloning is done to upscale the quantity of DNA. PCR uses primers and can be used to isolate and amplify the DNA up to the scale it is easily clonable.

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You may tell so. DNA amplification is a more generalized term for what you are indicating. Gene cloning with help of bacteria; popularly known as only Gene-cloning or Molecular cloning; is mainly used for gene or DNA amplification in vivo; and also PCR method (the most basic type) is also for DNA amplification, but in vitro, cell-free conditions.

But practically it may create some confusion; since the term "gene-cloning"/ "molecular cloning" popularly refer to that one done in living bacteria. (though the purpose or application is very same).

Reference: Wikipedia

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