Three siblings, one question
Each of us inherits roughly half our DNA from each parent, but which half is random. That means siblings, who share the same parents, can receive quite different ancestral segments. By testing three siblings, we get three different samplings of the same ancestral pool. The similarities confirm the shared heritage; the differences reveal the randomness of inheritance.
My brother Gervais and I tested with AncestryDNA; our sister Shirley with 23andMe. Despite the different platforms and methodologies, the results tell a consistent story. All three of us show the same broad pattern: roughly half our ancestry traces to the Indian subcontinent, about a quarter to Europe, about a fifth to Africa, and a smaller but significant component to Oceania and Southeast Asia, the Austronesian thread that connects us to Madagascar and ultimately to Borneo.
Ancestry comparison: three siblings
Gérard and Gervais were tested by AncestryDNA; Shirley by 23andMe. The two platforms use different reference populations and algorithms, yet the broad pattern is remarkably consistent across all three, confirming the underlying ancestry signal.
Gérard
AncestryDNA
Gervais
AncestryDNA
Shirley
23andMe
Four-region ancestry roll-up
Gérard's measured AncestryDNA, reconciled into four super-regions, built top-down from measured DNA and parental phasing, not predicted from ancestors upward. Where siblings agree, the reconstruction is confirmed.
Method: Maternal half derived from Angela's measured AncestryDNA ÷ 2, confirmed by Ancestry's parental phasing. Paternal half now measured directly via phasing: the two methods agree to within a point or two on every super-region.
DNA match explorer
Matching DNA to genealogy
Each ancestor contributes an expected share of DNA, roughly half per generation back (½ⁿ). Comparing that prediction against the measured AncestryDNA percentages tests the family tree against the genome. Where they align, the genealogy is confirmed. Where they diverge, there is more to find.
Indian-born, identified in records by an indenture number. The deepest confirmed Indian ancestor on the maternal side. The M2b maternal haplogroup traces through his daughter Camille.
Wife of Narsimloo and mother of Camille. Both of Camille's parents were Tamil, confirming Camille as essentially fully South Indian and strengthening the Indian signal on the maternal side.
Angela has directly identified Alcide as Malgache (Malagasy) — family memory, not a guess. Parental phasing of Gérard's DNA independently corroborates this, showing the expected Malagasy (Austronesian + Bantu) profile, with no European admixture: Africa ~5.75%, Austronesia ~6.75%, Europe 0%. His French surname was almost certainly imposed through the slave system. Family testimony and DNA phasing agree, even though the exact internal Bantu/Austronesian split remains a reconstruction.
Paternal great-grandfather. One of two documented Indian ancestors on the paternal side, though the paternal Indian total (31%) far exceeds what he and Amélina can explain alone.
Paternal great-grandmother. Approximately half western Indian. Together with Joseph Arnasalon, they account for some but not all of the paternal Indian signal.
Mother of Pierre Jérôme. Malagasy ancestry splits into Austronesian (SE Asia) and Bantu (African) DNA signals.
Probable father of Pierre Jérôme. Y-chromosome R-S219 traces to Leinster, Ireland, reflected in the Celtic and West-of-England signals.
A second Malagasy ancestor on the paternal line, father of Jenny Chaillet.
West African origin, seven generations back. Expected ~0.8%, measured 1% Senegal: a close match. AncestryDNA resolves the specific region.
A third Malagasy ancestor, wife of Charles Bocasse.
A fourth Malagasy ancestor, wife of Michel Mongelard. Birthplace Fort-Dauphin is explicitly recorded.
Documented French ancestor from Savoie, the clearest European paternal line beyond Galichet.
French colonial immigrant on strong inference: Isle de France had no European population before 1721 and only ~200 free colonists by 1735, an entirely imported population built by the Compagnie des Indes' 1726 settlement policy, plus his social role as a slave-owner who recognised his children by an enslaved woman. Exact French town or province remains unconfirmed hypothesis.
Enslaved woman, wife of Antoine Coré. Inferred South Indian based on period (French governors recruited South Indians directly from Pondicherry into the Mascarenes in exactly this window, a trade with a documented kidnapping element), Milbert's eyewitness account of Indian concubines in Mauritius, and the paternal Indian surplus in the DNA. Not documented individually.
French colonial immigrant on strong inference, by the same demographic reasoning as Antoine Coré. His "dit" name, mandatory for enlisted French soldiers from 1716, is itself strong inference that he served as a soldier before settling.
Enslaved woman, wife of Noel dit Lajoye. Same inference as Marie N: period, Milbert, and DNA corroboration. Together, Marie N and Catherine N represent two independent Indian-origin lines on the paternal side, supporting the picture of multiple distinct Indian ancestors rather than one source.
Husband of Marie Angéla David and father of Joseph Reginald Victorien (Angela's father). His own origin is undocumented. At least two of his children are remembered as blue-eyed, suggestive of European ancestry, though eye colour is governed by a handful of genes and is weak evidence of overall ancestry on its own (the same caution applies to grandfather Millen's pale complexion elsewhere in this project). On this basis, half of his theoretical 12.5% share (6.25% of Gérard's genome) is provisionally credited to Europe, and the other half is left unresolved. This is an educated guess, not a documented fact, and it accounts for most of the previously unexplained European gap, so it should be held to a high standard of caveat rather than treated as settled. His unresolved half remains genuinely undirected: unlike Antoinette Cangy (see below), there is no surname or other evidence pointing it toward Africa specifically, so Gérard leans toward Cangy rather than him as the more likely carrier of the maternal African residual.
Wife of Emile Jérome. Earlier speculation based on grandfather Millen's pale appearance suggested she might have been strongly European. However, the measured paternal DNA shows only ~8–9% total European, most of it already accounted for by Galichet and Mongelard. The large paternal Indian surplus (31%) suggests she more likely leaned Indian, consistent with the documented presence of Indian women in early colonial Mauritius.
Wife of Noël Brode Coret. The GEDCOM names her parents (Auguste Coret and Marie Françoise Guillaume), but they supply no meaningful origin or ethnic information, and the branch effectively dead-ends at her. Unlike the Coret–Mongelard line through her husband, where all eight G7 ancestors are identifiable, her own line goes dark. Her theoretical share (6.25%) was originally credited to Europe in full; Gérard has since revised this to a half-European hypothesis. His reasoning: no record shows any other Coret immigrant family arriving in Mauritius, so it's a strong inference that every Coret, including her father Auguste, descends from the single identified patriarch, Antoine Coré, some generations down. Since European women were rare in this colonial society outside separate free communities (such as Mauritius's free Indians), Auguste Coret and, most likely, Marie Françoise Guillaume were themselves probably already only half European rather than fully so, making Marie Ernestine also about half European, half other. Only half her theoretical share, ~3.125%, is now credited to Europe, revising attributed paternal Europe down to ~7.0% (from ~10.15%) against measured ~9%, and whole-genome Europe down to ~19.5% (from ~22.6%). This is an educated guess, not a documented fact, held to the same standard as the Louis Oscar Victorien hypothesis, and arguably resting on a longer inferential chain than the full-European reading it replaces. Her other, non-European half returns to the open, unresolved pool rather than Europe; it is a plausible but uncredited partial candidate for the paternal African plausibility note (previously her full share was, at ~78% coverage, before the revision), though Indian isn't excluded either — an enslaved Indian woman is already the working hypothesis for two other wives in this same line (Marie N, Catherine N), and only a numeric quirk (paternal Indian already has no spare headroom) mildly favours African/Malagasy over Indian for this half.
Father of Marie Angéla David (Angela's paternal grandmother). Family memory (via Angela) holds that Marie Angéla David was "half-white." Since her mother Antoinette Cangy bears a surname rooted in slavery, the European half most likely entered through Joseph Seblin David. This is an educated guess, not fact: "half-white" reflects family perception rather than documented descent, and the surname David is suggestive but not proof of European origin.
Mother of Marie Angéla David. Her surname Cangy is rooted in slavery, indicating she was of enslaved African, Malagasy, or Indian descent — but which, and in what proportions, is not documented. A surname-distribution check found Cangy essentially unique to Mauritius worldwide (~504 bearers, its largest population by far, with only marginal diaspora numbers in France and Australia) — consistent with a name locally coined for someone of enslaved descent, fitting Gérard's recollection that such names were assigned at the 1835 emancipation (though no source confirms this for Cangy specifically). **Reclassified:** her full theoretical share (6.25%) is now credited to Africa outright, rather than left as a leaning — it fits cleanly against the maternal African headroom (attributed 5.75% vs measured ~12.5-13%) and closes most of the remaining African gap. This is an educated guess, not a documented fact, held to the same standard as the Louis Oscar Victorien and Marie Ernestine Coret hypotheses, and should always carry that caveat.
Reading the numbers: Expected percentages assume even inheritance, but DNA recombines unevenly, so measured values scatter around the expectation. Multiple ancestors from the same region stack together. The five Malagasy ancestors (Alcide François on the maternal side; Jeanne Clarisse, Vendredi Chaillet, Marie Jeanne Béthune, and Marie Madeleine on the paternal side) jointly account for the 9% Southeast Asian signal plus part of the African Bantu signal, because Madagascar's own population is a blend of Austronesian and Bantu ancestry.
What the sub-regions reveal
The broad continental categories tell one story; the sub-regional breakdowns tell a more specific one. Within the Indian component, the largest contribution comes from Southern India, consistent with the historical record of enslaved women brought from Pondicherry and other French Indian trading posts during the colonial period.
Within the European component, the strongest signal is from Ireland, Scotland, and Wales, which aligns with the Y-chromosome haplogroup evidence tracing the paternal line to Leinster. The French component, which one might expect to dominate given Mauritius's colonial history, is present but smaller.
The African component shows Southern Bantu as the largest sub-group, with East African contributions, consistent with the known sources of enslaved people brought to Mauritius from Mozambique and the East African coast. The Oceania and Southeast Asian component, though the smallest at around 7–8%, is perhaps the most remarkable: it traces to the Northern Philippines and the broader Austronesian world, carried to Mauritius via Madagascar.
Deep ancestry: the paternal line
The Y-chromosome passes from father to son essentially unchanged, allowing us to trace the direct paternal line deep into the past. My Y-chromosome haplogroup is R-S219, which traces back through the Jerome line: through my father Noel, his father Millen, back through Jean-Baptiste, Emile, and Pierre Jerome, to the question mark that is Jean-Pierre Galichet.
If Galichet was indeed Pierre Jerome's biological father, as the circumstantial evidence strongly suggests, then R-S219 tells us where Galichet's own paternal line originated. This haplogroup traces to a king in Leinster, Ireland, around 300 AD. The Irish connection, unexpected for a man with a French name in colonial Mauritius, is confirmed by the sub-regional DNA breakdown showing Ireland/Scotland/Wales as the strongest European component.
Deep ancestry: the maternal line
Mitochondrial DNA passes from mother to child, allowing us to trace the direct maternal line. My maternal haplogroup is M2b, traced through my mother Angela, her mother Irene François, and her grandmother Camille Narsimoulou.
The M2b haplogroup traces to South India, to the Dravidian peoples. This is consistent with the historical record: the maternal line traces back through women who were brought from Southern India to Mauritius during the colonial period, part of the largely undocumented story of Dravidian women in the slave and indentured labour systems. The surname Narsimoulou itself points to Tamil or Telugu origin.
Paternal line: Y-chromosome R-S219
Maternal line: mtDNA M2b
Phasing: separating the strands
Standard ancestry tests report a blended average of your maternal and paternal inheritance. But by testing multiple family members and comparing which DNA segments are shared, it is possible to "phase" the data, working out which segments came from which parent.
AncestryDNA provided initial phasing using data from myself, Gervais, and our mother Angela. Two paternal first cousins have also been tested by Ancestry, providing their geographic ancestry breakdowns which help confirm the paternal line's composition. Further phasing work is underway using my full genome sequence from Full Genomes Corporation, which will allow finer-grained separation of maternal and paternal segments across all chromosomes.
The phasing work also enables exploration of IBD (Identical By Descent) segments, stretches of DNA shared between individuals that indicate a common ancestor. Hidden Markov Model methods can detect these shared segments, connecting the DNA evidence directly to the family tree.
Explore further
How phasing works
An accessible explanation of the methodology for separating maternal and paternal DNA using family data.
Chromosome viewer
See which ancestral components sit on which chromosomes, with maternal and paternal sides separated.
IBD explorer
Shared DNA segments between family members, the genetic evidence connecting the family tree.
Methodology
How the measured DNA is worked down into the family tree, step by step, and every assumption behind the attribution figures.
This strand connects to