As you might know, a man gets his Y-chromosome exclusively from his father (his mother doesn't have one). In North Africa, your ethnic/tribal/familial/etc identity – an important predictor of your language – is likewise traditionally supposed to be inherited from your father, not your mother. So it's illuminating to compare them.
A haplotype called E-M81 (or E1b1b, E3b) is frequent in Northwest Africa, and is held by large majorities of the Berber-speaking populations examined in Morocco or in the western/central Sahara; it is much less frequent in the Middle East. It seems reasonable to associate this haplotype with the spread of Berber. By contrast, haplotype J1 is very frequent in the Arabian Peninsula, but gets rarer and rarer as you go west; it seems reasonable to associate this haplotype with the Arab expansion. (Neither Berbers nor Arabs were ever completely homogeneous, so other, less frequent haplotypes may also be associated with one or the other of these events.)
The table gives four Algerian populations: Oran, Algiers, Tizi-Ouzou (Kabyle), and Mozabites. Mozabites, as might be expected, have a really high frequency of E-M81 (87%) and a really low frequency of J1 (1.5%). The other three, however, all have about 45% E-M81 (45%, 43%, 47% respectively) – in terms of the frequency of this presumably Berber marker, there is almost no difference between the Arabic speakers of Algiers and Oran and the Berber speakers of Tizi-Ouzou. In terms of the frequency of the originally Arab J1, the difference is hardly greater – 23% in Oran and Algiers vs. 16% in Tizi-Ouzou. Since we aren't sure about the historical interpretation of the rest of the haplotypes found, it may be more useful to consider the ratios of "Berber" E-M81 to "Arab" J1: 2:1 for Oran and Algiers vs. 3:1 for Tizi-Ouzou (and 29:1 for Mozabites).
What this tentatively tells us, in brief, is that:
- In Algeria, plenty of Berber fathers adopted Arabic; if you are an Arabic speaker, you're very likely patrilineally Berber. (No surprise there!)
- In Kabylie, a fair number of Arab fathers adopted Berber; if you are a Kabyle speaker, you may well nonetheless be patrilineally Arab. (Many readers will be surprised by this, but they shouldn't be: read about the history of the Sebaou valley in and after the Turkish period sometime, for example, let alone the more controversial example of the maraboutic families.)
- Arabic was more likely to be adopted where more Arabs had come in, even though genetically, Arabs remained a minority. (In other words, Arabisation wasn't just about language shift.)
- It's really rare for an outsider man to become Mozabite. (No surprise there either.)
Finally, one Berber-speaking population stands out radically in this table: Siwa. There is no significant presence of E-M81 there, and not much J1 either. The haplotypes best represented there are R1b – usually associated with Western Europe and, for some reason, with Chadic speakers – and B2a1a, usually associated with central and eastern sub-Saharan Africa. R1b has a reasonable frequency in Kabylie and Niger Tuareg, and to a lesser extent in Egypt, so we might suppose that it reflects the oasis' Berber roots, or that it reflects immigration from the east; we'd need non-Tuareg Libyan Berber genetic data to test that hypothesis. B, however, isn't common anywhere else in North Africa; does it derive from the slave trade, or from some older population of the region? Again, I think more data from Libya will be needed to make sense of this.