The Y chromosome is inherited, virtually unchanged, from biological father to biological son across generations. In a continuous unbroken paternal line, a descendant today would carry a Y chromosome closely related to that of a seventeenth-century ancestor. The absence of a match between Beethoven’s Y chromosome and those of the living men who share his documented paternal genealogy means that the biological and the documented lineages diverged at some point.
The researchers identified the window in which this divergence must have occurred: somewhere between the conception of Hendrik van Beethoven in 1572 and the conception of Ludwig van Beethoven in 1770—a span of approximately seven generations.
The most probable explanation for such a divergence, in genetic genealogy, is what researchers call an extra-pair paternity event: a situation in which a child was born to a woman who was married to one man but was biologically fathered by another man. In the documentary record, the child was recorded as the husband’s. In biological reality, the child carried a different Y chromosome, which then propagated forward in the family line to Ludwig.
The study did not identify which generation this event occurred in. It did not name any specific individual as the biological father, or identify the woman involved, or establish the circumstances of the conception. The seven-generation window covers multiple individuals about whom the historical record contains varying degrees of information. Without evidence from that specific generation—DNA from identifiable remains, documentary evidence of infidelity or illegitimacy—the exact placement cannot be determined.