Coefficient de consanguinité: comment le calculer

Coefficient de consanguinité: comment le calculer

Coefficient of inbreeding: how to calculate it

by Un brin d'ADN · View the channel on PSI

Life & Natural Systems Biology PSALife sciences: general issuesPSAKGenetics (non-medical)
🎙 Un brin d'ADN 👥 790 📅 February 26, 2024 ⏱ 18 min 👁 6K 📄 tutorial 🧭 2026-10-09
Available in: English (current) Français

Keywords

inbreeding coefficientBallou formulapedigreegenetic genealogyconsanguinity

Summary

The video ‘Un brin d’ADN’ offers a step-by-step tutorial on calculating the inbreeding coefficient (COI) using the formula by J.D. Ballou (1997). The author defines the concept of a common ancestor, emphasizes that it must be illustrated only once in the pedigree, and explains the need to calculate the prior inbreeding of common ancestors. The method involves identifying loops (paths from the individual to a common ancestor and back) without passing through the same individual twice. The formula applied is 0.5^n multiplied by (1 + inbreeding coefficient of the common ancestor). A complex example is worked out: a pedigree with three common ancestors (C, E, and A), and a prior inbreeding coefficient for C. This step-by-step calculation yields a total coefficient of 0.20315 (approximately 20%) for the target individual X. The video also provides typical coefficient values: first cousins (6.25%), half-siblings (12.5%), parent-offspring (25%), and notes that some dog breeds like Schnauzers and Beagles have average levels of 25%, while Bull Terriers reach 50%. Finally, it mentions the health risks linked to elevated coefficients, citing a 2011 study on first cousins and a 2016 study on dog breeds, and relates the topic to marriage dispensations in Quebec’s Catholic genealogy.

199 words

Critical Evaluation

Value of the Information & Strength of the Argument

The value of this video lies in its clear, methodical pedagogical approach to a technical genetic calculation. It progresses logically from basic definitions to complex multi-loop examples, reinforcing each step with written formulas. The argumentation is sound: it respects the proper sequence of calculations (computing the inbreeding of a common ancestor before that of the target individual) and explicitly warns that the Ballou formula overestimates real genetic inbreeding, thus acknowledging its limitations without undermining its pedagogical utility.

Scientific Rigor, Source Quality, Title Accuracy

The scientific rigor is good. The video is anchored in a specific, cited formula (Ballou, 1997) and references two empirical studies (2011 on human first cousins, 2016 on dog breeds) to provide context for the calculated values. The title is perfectly aligned with the content, accurately reflecting the instructional nature of the video. The methodology is transparent; the author explains each step of the pedigree analysis and the mathematical operations, ensuring the viewer can reproduce the calculation.

169 words

Title / Content Match

The title is perfectly accurate, as the video indeed explains how to calculate the inbreeding coefficient with a detailed example.

Quality & Reliability

8/10

The video provides a clear, step-by-step tutorial on a well-established formula (Ballou, 1997), and notably includes an important caveat about its limits, which demonstrates scientific honesty. The examples are precise and reproducible.

Chapters

Cited Sources

  • Formula by J.D. Ballou (1997) — The core formula used for calculating the inbreeding coefficient in this tutorial.
  • Study on first-cousin congenital malformations (2011) — Referenced to estimate the doubled risk (4-6% vs 2-3%) for offspring of first cousins.
  • Study on dog breed inbreeding (2016) — Mentioned regarding high average inbreeding levels in Schnauzers, Beagles, and Bull Terriers.

Concurring Sources

Contribution & Novelties

This video’s original contribution is its clear, worked-out pedagogical example combining multiple loops and prior inbreeding within the same pedigree, which is often harder to grasp from textbooks alone. It demystifies the step-by-step application of Ballou’s formula for a general audience interested in genetic genealogy, while correctly cautioning about its limitations.

Pour aller plus loin :

  • Inbreeding — Overview of the biological concept and its effects.
  • Pedigree collapse — Key concept explaining why an ancestor appears multiple times in a pedigree.
  • Inbreeding depression — The biological consequences of reduced genetic diversity, directly relevant to the risks discussed.
  • Coefficient of relationship — Mathematical basis for kinship and inheritance probabilities.

108 words

Radar Profile

The radar profile shows a strong fiabilité_globale score (9) reflecting scientific honesty, with high technical level (8) and good information quality (8), though quantity is moderate (7) given its concise 18-minute format.

Reliability 9/10