Ancestral DNA & Kinship Transmission Decoder

Ancestral DNA & Kinship Decoder: How Much of Your Italian Ancestor Actually Lives in You?

This free decoder calculates the statistical share of autosomal DNA you inherit from any direct ancestor — and from collateral relatives such as aunts, uncles and cousins — together with the honest centimorgan ranges behind each average. It also translates every relationship into the two calendars of kinship that governed Italian families for centuries: the degree counted by the Italian Civil Code (articles 74–76) and the degree counted by Catholic canon law — the single step of difference that decided matrimonial dispensations, inheritances and parish margins. Enter the ancestor you know from a document and the connection of the person in your hand: the board returns the share, the two degrees, and a generation-by-generation decay chart.

How it works

• Input: a known direct ancestor (parent to 3rd great-grandparent) and the connection of the documented person to that ancestor (their parent, grandparent, sibling or child).
• Calculates: the generations between you and the documented person, the expected autosomal share (halving at every transmission), and the civil-law and canon-law kinship degrees.
• Returns: the average share with its real centimorgan range, both kinship degrees, and a decay board showing exactly where the biology goes silent and the paper takes over.
• Important: averages are not proofs. From the sixth generation upward there is a real probability of sharing zero detectable DNA with an ancestor who is fully documented on paper.

Frequently asked questions

How much DNA do I share with a second cousin?
About 3.1% on average — roughly 230 centimorgans — with a real range from 46 to 515 cM. In genetic genealogy, ranges matter more than averages: two true second cousins can sit at opposite ends of that range and still be true cousins.

Why does my DNA test show no match with a documented relative?
Because autosomal DNA is redistributed by random crossovers at every transmission. From a 4th great-grandparent upward there is a real and growing probability of inheriting zero autosomal DNA from that specific ancestor: the paper ancestor outlives the genetic one. Both facts are true at once.

What is the difference between civil and canon-law kinship degrees?
The Italian Civil Code counts the births in both lines, up to and down from the common root (siblings are 2nd degree, art. 75); canon law counts only the distance from the common root (siblings are 1st degree). That single step is what made a marriage dispensable — or not — in a parish court, and dispensation files are often the richest genealogical document in a parish archive.

Can DNA prove my Italian line?
No. DNA suggests; registers prove. A shared segment can point to a common couple, but only a baptism, a marriage or a notarial act names them. The decoder tells you which register to ask for — and the house retrieves it.

Key terms

• Centimorgan (cM): the unit measuring how much DNA two people share; higher values mean closer relationships.
• Autosomal DNA: the 22 chromosome pairs inherited from both parents, recombined at every generation.
• Meiotic recombination: the random crossover that shuffles each parent's chromosomes — the reason siblings inherit different shares of the same ancestors.
• Consanguinity dispensation: the canon-law permission required when a couple fell within the prohibited degrees of kinship.

Methodology & sources

Averages and ranges follow the Shared cM Project (Bettinger, 2020, tool v4) and the relatedness literature (Speed & Balding, Nature Reviews Genetics, 2015). Kinship degrees follow the Italian Civil Code, articles 74–76, and the Codex Iuris Canonici. This decoder is one of three free benches in the house's reading room, alongside the surname map and the military service checker.