Ancestory

DNA & ancestry: what the tests can and can’t tell you

Ancestry DNA is powerful and heavily oversold. This page explains the three kinds of test, the hierarchical haplogroup system they use, and how genetic ancestry connects to peoples, cultures, places and time — with the caveats the marketing usually drops. One rule runs through all of it: genetics here is population-level and probabilistic. It reveals broad, deep patterns shared by millions; it does not hand you a nationality, a clan, or a tidy pie-chart of “who you are”.

1 · The three tests read different parts of your ancestry

Y-DNA — the direct paternal line

Passed father → son almost unchanged; only males carry a Y chromosome (a woman tests a father or brother). It traces exactly one line — your father’s father’s father — which makes it excellent for deep paternal origins and surname projects. Its blind spot is everything else: ten generations back you have around 1,024 ancestors, and Y-DNA follows just one of them.

mtDNA — the direct maternal line

Passed mother → all her children almost unchanged; everyone carries it. It traces one line — your mother’s mother’s mother — and is powerful for deep maternal origins, with the same single-line blind spot.

Autosomal DNA — everyone, but fading

The 22 non-sex chromosomes, inherited from all your ancestors — but roughly halved each generation (~50% a parent, ~25% a grandparent…), so beyond about 5–8 generations many ancestors leave no detectable trace. It powers relative-matching and recent genealogy, and it is what “ethnicity estimates” are built from. The honest caveat there: ethnicity percentages are probabilistic comparisons against a company’s own reference panels — low-resolution, company-specific, and revised as the panels change. Absence of a label (say, “0% Iberian”) is not absence of that ancestry; it’s the limit of the method. The same saliva can return different numbers from different companies.

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☐ male · ◯ female. The two single-line tests each follow one edge to the top of the tree; autosomal DNA comes from the whole tree but thins with depth — which is why it can’t reach far back, and why Y/mt reach deep but only along one line.

2 · The hierarchy: haplogroups form a tree

Y-DNA and mtDNA are sorted into haplogroups, and haplogroups form a branching tree. Every so often a harmless mutation arises in one man’s Y (or one woman’s mtDNA) and passes to all descendants; each mutation defines a branch. So haplogroups are nested — you belong to a broad, ancient one and all its finer subclades at once (a man might be R, and R1, and R1b, and R1b1a1b, and R-L21 — each a deeper twig on the same branch) established [isogg] :

The hierarchy is time: broad haplogroups are old (splits tens of thousands of years deep); narrow subclades are young. Reading down the tree reads forward in time — and often tracks a migration.

Browse all haplogroups → — a complete index of the Y-DNA and mtDNA haplogroups, with pages for the major ones.

3 · Linking DNA to people, culture, place & time

This is where genetic ancestry meets history — and where it’s most abused. Haplogroups correlate with populations, but a haplogroup is not an ethnicity, a nationality or a clan. Yet plot ancient DNA across time and place and real historical events appear. Here is Britain and Ireland’s own male line (Y-DNA), period by period — every figure computed by us from the open ancient-DNA record:

0 25 50 75 100 I2 — Mesolithic: 83% R1b — Mesolithic: 17% Mesolithic pre-4000 BCE n=6 ⚠ I2 — Neolithic: 93% R1b — Neolithic: 1% other — Neolithic: 7% Neolithic 4000–2450 BCE n=200 I2 — Bronze Age: 12% R1b — Bronze Age: 84% other — Bronze Age: 5% Bronze Age 2450–800 BCE n=111 I2 — Iron Age: 4% G2a — Iron Age: 4% R1b — Iron Age: 88% other — Iron Age: 4% Iron Age 800 BCE–AD 43 n=159 I2 — Roman: 8% G2a — Roman: 2% R1b — Roman: 83% other — Roman: 8% Roman AD 43–410 n=53 I2 — Early Medieval: 8% G2a — Early Medieval: 1% R1b — Early Medieval: 55% R1a — Early Medieval: 5% I1 — Early Medieval: 23% other — Early Medieval: 8% Early Medieval AD 410–1066 n=192 I2 — Medieval+: 1% R1b — Medieval+: 17% R1a — Medieval+: 2% I1 — Medieval+: 4% other — Medieval+: 76% Medieval+ AD 1066–1800 n=161 % of male samples
Y-DNA (paternal line) haplogroup frequencies among ancient male samples from Britain & Ireland, by period — computed by us from the Allen Ancient DNA Resource (CC0). Small-sample periods (marked ⚠) and the large “other / unresolved” share in later periods are shown honestly: this is real, uneven data, not a tidy story.

Read it left to right and the deep history is visible:

The maternal line (mtDNA) tells a related but different story — a reminder that the two single-line tests can diverge, because they trace different ancestors:

0 25 50 75 100 U5 — Mesolithic: 82% H — Mesolithic: 9% other — Mesolithic: 9% Mesolithic pre-4000 BCE n=11 ⚠ U5 — Neolithic: 14% U4 — Neolithic: 0% K — Neolithic: 31% H — Neolithic: 19% J — Neolithic: 9% T — Neolithic: 10% other — Neolithic: 17% Neolithic 4000–2450 BCE n=263 U5 — Bronze Age: 17% U4 — Bronze Age: 3% K — Bronze Age: 15% H — Bronze Age: 28% J — Bronze Age: 7% T — Bronze Age: 15% other — Bronze Age: 15% Bronze Age 2450–800 BCE n=215 U5 — Iron Age: 11% U4 — Iron Age: 3% K — Iron Age: 10% H — Iron Age: 41% J — Iron Age: 10% T — Iron Age: 10% other — Iron Age: 15% Iron Age 800 BCE–AD 43 n=324 U5 — Roman: 29% U4 — Roman: 1% K — Roman: 9% H — Roman: 41% J — Roman: 15% T — Roman: 3% other — Roman: 1% Roman AD 43–410 n=75 U5 — Early Medieval: 12% U4 — Early Medieval: 2% K — Early Medieval: 9% H — Early Medieval: 40% J — Early Medieval: 9% T — Early Medieval: 12% other — Early Medieval: 16% Early Medieval AD 410–1066 n=218 U4 — Medieval+: 13% H — Medieval+: 63% J — Medieval+: 13% other — Medieval+: 13% Medieval+ AD 1066–1800 n=8 ⚠ % of male samples
mtDNA (maternal line) haplogroup frequencies among ancient samples from Britain & Ireland, by period — computed by us from the Allen Ancient DNA Resource (CC0). Small-sample periods (marked ⚠) and the large “other / unresolved” share in later periods are shown honestly: this is real, uneven data, not a tidy story.

Each lineage ties to a people, a material culture and a place at a time — the Beaker culture, the incoming “Anglo-Saxons” — the thread this site follows: DNA → population → culture → place → time, with the uncertainty kept in view.

4 · What this can — and can’t — tell you

Sources