Use of which in a sentence

The two variants are both grammatical.

(1) has 'a recombination model' (correctly offset, as it is a non-defining parenthetical, by commas) as an explicative / descriptive appositive.

(2) uses a non-defining relative clause (correctly, as it is non-defining, set off by commas) to add the additional information.

Both are correct.

In 1, “SRH” and “a recombination model” are in apposition, suggesting an equivalence between them. The equivalence need only be partial. Thus, all that we know about SRH is that it is a member of the set of recombination models; all we know about the set of recombination models is that it contains SRH. The same analysis could be done with “I saw a tree, a green thing” or “I saw a green thing, a tree”. In each example the overlap of equivalence is partial.

In 2, “which is a recombination model” is separated from the main flow of meaning (“SRH is used ...”) by commas. It is therefore a supplementary clause that qualifies SRH. The logical considerations of partial equivalence still apply.

I conclude that both are clear, unambiguous and correct and that there is no difference in meaning.