Talk:Consanguinity

Untitled
I'm gonna try to work on this article in more detail in the coming weeks. Feel free to help. Also, I may change the chart I made. --Doctorcherokee 01:16, 3 Dec 2004 (UTC)

I wrote this:


 * Consanguinity is measured by degrees of consanguinity, which can be defined in several different ways. The most common definition is the modern civil law definition, which increases by one with each step up or down along the shortest path between two individuals in a family tree; thus, for example, you are one degree from either parent, or from your children; two sibilings are two degrees apart -- one step up to the common parent, another back down to the sibling. This is also the definition used in Roman law.


 * Degrees of consanguinity defined in this way are directly related to the probability of the two individuals sharing a given gene, where the probability is $$2^{-n}$$ where $$n$$ is the number of degrees of consanguinity. For this reason, breeding with someone with a close degree of consanguinity carries an elevated risk of genetic problems due to inbreeding.

Now I'm not so sure that this is accurate, so I've taken it out. Does anyone know
 * 1) the accurate legal situation, for various jurisdictions and religious traditions?
 * 2) the correct biology and genetic probabilities?

For example, siblings share two direct common ancestors (mother and father): do they get a "double dose" of shared genes, so should n be 1 in this case? What about other more complex cases? -- The Anome 00:27, Feb 1, 2005 (UTC)

Aha. This should shed a bit more light on the subject... -- The Anome 00:29, Feb 1, 2005 (UTC)

OK, I now see that my previous treatment was half-baked, and plain wrong for siblings etc. However, considering the relationship of the various non-genetic schemes to the distance measured by the coefficient of consanguinity, and considering the "background noise" levels of the coefficient of consanguinity in the general population should provide an excellent scientific counterpoint to the religious, legal and historical story of consanguinity. This could be an excellent article! -- The Anome 00:46, Feb 1, 2005 (UTC)

Thoughts
It should be noted here that the chart doesn't follow the "intuitive fractions" people often employ when discussing this: siblings equal 100%, parents and children 50%, grandparents 25%. The up a step down a step makes sense for cousins and aunts and uncles (the latter technically 50% if they are 100% to mom or dad) but it doesn't seem right for siblings. If anything they should be ranked zero--as close a genetic match to us as is possible. Marskell 15:29, 29 August 2005 (UTC)
 * I think that you're right, siblings should not be less related than parents, however, I don't know if they more. -- Kjkolb 09:23, 22 October 2005 (UTC)

Cousin Chart
Another view: http://www.totemconsulting.ca/Consanguinity.html — Preceding unsigned comment added by Alfredsimpson (talk • contribs) 04:21, 28 May 2016 (UTC)
 * I think merging the 2 articles is a bad idea. I vote NO. Dr U 07:20, 3 February 2006 (UTC)
 * Merging the two articles is a bad idea because there can be innumerable consanguinity charts; the Cousin Chart is only applicable to consanguinity in the system of English speakers of European ethnicity. To include this chart within the Consanguinity article would invite the inclusion of the countless other consanguinity systems, which has the potential of making the article too bloated.  Instead, the Cousin Chart article should perhaps be renamed English Language Consanguinity System, which would allow future articles concerned with other consanguinity systems.  I vote NO.  Too Old 18:16, 3 February 2006 (UTC)

"Also, at a genetic level, half-fourth cousins typically do not exhibit greater genetic similarity with one another than with any other individual from the same population." - It seems to me, that paternal 4th cousins (probably sharing the same last name), would probably also share one complete chromosome in common, at least. (About %2 of genetic material?) — Preceding unsigned comment added by 69.124.116.101 (talk) 18:17, 5 March 2020 (UTC)
 * Yes, that would be true, if (I assume this was the assumption), both of them were male; but, since males cannot produce offspring with other males, and since Y-chromosome genes never enter the female population, "Y-chromisome consanguinity" is not of any importance..
 * However, your post got me thinking about another, slightly related (no pun intended) phenomenon, that may or may not be of any significant consideration (I am no mathematician ;) in the case of full sisters and half sisters who share a father, they all have identical copies of one of their X chromosomes. Therefore, wouldn't that mean that a boy and girl pair of cousins from two sisters would share a greater number of genes than would a boy and girl pair of cousins from a brother and a sister? 2600:1702:4960:1DE0:A183:7336:D574:C480 (talk) 10:22, 4 December 2021 (UTC)
 * EDIT: for simplicity's sake, in the aforesaid hypotheticals, for the two cousins offspring from a brother and sister, let the boy be the brother's son and the girl the sister's daughter. I think there's fewer X chromosomes needing to be accounted for that way :)

Degrees of Consanguinity
I'm pretty sure that the 4th degree of consanguinity is between first, not fourth cousins

Actually it is. Ego -> Parents -> Grandparents -> Aunt/Uncle -> Cousin --Sven Lotz 11:42, 14 July 2007 (UTC)

[I added a pdf. link] "The TABLE of Degrees of CONSANGUINITY and AFFINITY" enacted by Pennsylvania Law in the year 1705, found in "The Legislative Reference Bureau, an agency of the Pennsylvania General Assembly," a publicly available web site: http://www.palrb.us/default.asp

Joe Menkevich - local history researcher in Philadelphia. Bigjoe5216 09:04, 9 October 2007 (UTC)

Expert attention needed
I came here looking for info on aunts, uncles, nieces, and nephews. Some or all of those words are redirected to the related article Cousin, but that article is very light on covering them. Looking at Cousin and this article and their talk pages, it seems that both articles are pretty weak. I think somebody needs to come in and clean house. Sibling could use a bit of housecleaning, too. Lou Sander 22:06, 9 February 2007 (UTC)

My name Is Dr Michael Black, Curator for www.consang.net on behalf of Consanguinty expert, Prof. Alan Bittles. I have added a paragraph on he genetic definition of Consanguinity and added external links to the Consang.net database. This has recently been made into a wiki and is being updated, with exciting updates planned for the near future. --Dr Michael Black 08:09, 27 April 2007 (UTC)

Presuming that's the section under 'Genetic definition', I have to say that I found it jarringly out-of-place with the tone of the rest of the article, being highly technical and with no definition of its terms. That said, I appreciate the attempt to provide some genetic background to the subject of - literally - mixed blood, where the remainder of the page is legal / cultural in its emphasis.

I do find the article itself rather light on solid information about the subject, and it certainly didn't help me to find the information I wanted: having read (on the Cousin page) about the percentage of consanguinity between first cousins, I simply wanted to know why the percentage given (0.125%) was half what I would naively expect (0.25%). I would really appreciate some (entry-level!) information on how consanguinity is calculated between individuals. This article on GeneWeb was the best I could find on the subject with a quick Google search. CuriousHybrid 16:18, 29 October 2007 (UTC)

The Knot System explains exactly how to measure consanguinity using what Hojrup calls KinCodes, and it is very simple even for complex relationships where there are multiple common ancestors. You count the steps from the proband (ie, yourself, up to the common ancestor then back down to the other person. You don't count yourself of the other person, you count the common ancestor going up and down.  Example, first cousins.  Me to Grandpa:  2.  Grandpa to cousin:  2.  Total:  4.  Call that total value N.  Consanguinity is (1/2)^N or 1/16.  But we also have Grandma in common.  That calculation also results in 1/16.  Add up all the consanguinity, 1/16 + 1/16 = 1/8.

To answer CuriousHybrid's question, why do first cousins share 0.125 (1/8th) and not 1/4? 1/4 is the amount of genes you have in common with your full sibling (self to mother: 1. mother to sibling = 1. N = 2.  (1/2)^2 = 1/4.  repeat for father.  1/4 + 1/4 = 1/2). A non-mathematical way of answering the question is that even though siblings have both parents in common, they each get a different 1/2 of the parents' genetic material (marvels of genetic recombination), 1/2 of which is overlapping from sibling to sibling. 67.175.124.153 (talk) 04:01, 12 January 2009 (UTC)

Genetic Disorders
I've added a section on the increased risk of autosomal recessive disorders in consanguinous relationships. --Mike Burden (talk) 11:51, 27 April 2008 (UTC)

Table of CONSANGUINITY needed
The table shown in the article is a table of relationships, not a table of consanguinity. A table of consanguinity shows the degree of relationship between two individuals, not just the name of their relationship to one another. For example, a person is related in the second degree to his/her grandchildren. A person is also related in the second degree to his/her siblings. I've added an external link to a real table of consanguinity. As there are two ways to compute degrees of collateral consanguinity-- by civil law and by canon law (church)-- there need to be two tables of consanguinity shown in the article. —Preceding unsigned comment added by 12.76.129.17 (talk) 15:36, 22 August 2008 (UTC)

Legal Application needed
The page would benefit from a discussion of how consanguinity is applied under common law and statute beyond probate. For instance, how it is used for determining prohibitions on nepotism. Also, how consinguinity is applied to a spouse and the spouse's relations. AusJeb 15:46, 10 December 2008 (UTC)

Genetics needs a complete rewrite
The genetics section needs a complete rewrite, because it ignores the crucial issue that genes are inherited in blocks (as chromosomes). So for example, the boundary of F >= 0.0156 for consanguinity isn't arbitrary. It is the boundary at which the probability fallss below 0.5, that a male and female parent would share an identical chromosome (modulo any intervening mutations) that they could pass to a child. There are other similar errors in this section. This has ramifications throughout the article, wherever it talks of percentage of shared genes - it should be talking about probability of sharing a gene (the difference is minor up to second degree, but becomes increasingly important for more distant relationships).

By the way, this is one reason that a technical genetics section continues to be needed in this article - there's too much misunderstanding of these issues 'out there', it's not hard to find talk of miniscule levels of shared genetics between fourth cousins.

If no-one objects in the meantime, I'll put some effort into tidying up these issues in January when I have some free time. Urilabob (talk) 03:39, 20 November 2010 (UTC)


 * due to crossovers chromosomes are not inherited unchanged. For example a woman has two Xs.  She gives an X to her daughter.  She doesn't give one of her two Xs; she gives an X made from parts of her two Xs.  — Preceding unsigned comment added by 68.34.239.79 (talk) 06:08, 29 June 2012 (UTC)

Religious and traditional law
"In 1215 the Fourth Lateran Council made what they believed was a necessary change to canon law reducing the number of prohibited degrees of consanguinity from seven back to four.[8] The method of calculating prohibited degrees was changed also.[9] Instead of the former practice of counting up to the common ancestor then down to the proposed spouse, the new law computed consanguinity by counting back to the common ancestor.[9] <...> ...the need for dispensations was greatly reduced.[10]"

So we have a contradiction...

Before 1215: 7 degrees prohibited and "Roman" calculation rule. In this case 3rd cousins can marry (8th degree).

After 1215: 4 degrees prohibited and "Germanic/Canonical" calculation rule. In this case 3rd cousins may not marry (4th degree).

The method of calculation was not changed in 1215. "Germanic/Canonical" calculation rule was adopted earlier. — Preceding unsigned comment added by 213.87.142.15 (talk) 10:22, 10 September 2013 (UTC)

Percentages
The percentages do not seem correct. All direct male lines share 50% dna from the y chromosome.

The calculations are different for females.

This page does not reflect that in the chart.

I like to say "Boys are daddy (Y) and a little bit of pot luck (X). Girls are pot luck (X)."

It says 50% of X comes from the father and 50% from the mother given. There are dominant, co-dominant, recessive, etc., i.e. my sister has more British and Irish than my mother and I have less than my mother or something like that.

Looking at our chromosomes, I received an email where the individual believed my younger sister to be my aunt and my mother's sister, not mine.

My sister shows regions that I do not because she may have one more marker consistent with that group making her look like and member, whereas I may lack one marker.

Some markers she did not get at all from our father and I received all of his that were similar, whereas she received none, so I look consistent with 4 other genetic groups that she does not appear to belong to.

Her genetic matches are thousands more than mine.

It's not nearly as cut and dry.

However, it may be possible to say more about a direct male line.

It used to be expected that if a woman was widowed an unwed brother was expected to wed the widow. That brother could be more than a 50% dna match depending on which x chromosomes that received. Not to say that two brothers are the same or that the brother would even make for an agreeable marriage.

My youngest sister and I are very different individuals. Growing up people said they didn't even see a familial resemblance.

However, she does match a good bit of both family trees, but there are individuals that she does not tie to genetically for some roll of the dice reason.

There are only two finite combinations of the same two chromosomes. If a married couple could realize all combinations + 1, they could have identical children that are not twins.

I annoy people when I say the human race is finite. I suspect that mutations are not common enough for this not to be the case. And the idea of mutating dna probably means there will be a coupled shift or counter posing mutation that would cause a whole other series of issues.

However, I suspect that there is a purpose for all markers. Some people may have opinions on which are desirable or undesirable or combinations thereof. However, I doubt anyone is really smart enough to understand all of that. However, surely there are those who taut they do. :-)) — Preceding unsigned comment added by 67.245.53.92 (talk) 09:04, 16 April 2017 (UTC)
 * Your observations are incorrect. The Y chromosome accounts for less than 1% of the total base pairs in the human genome in men. See here. Nearly all the rest is diluted by 50% in every human reproduction. Males generally inherit 100% of Y-DNA from their fathers. Chris55 (talk) 15:34, 12 May 2017 (UTC)
 * This is not a page for general discussion of the subject. Please discuss concrete improvements to the article, based on reliable sources, discussed in light of the policies and guidelines. Thanks. Jytdog (talk) 16:42, 12 May 2017 (UTC)

Level of lineal consanguinity = meiosis?
This article states:

"...consanguinity table in which each level of lineal consanguinity (generation or meiosis) appears as a row..."

Is the parenthetical remark correct? Does each level of lineal consanguinity equal generation or meiosis, especially the latter, which has to do with chromosomes? If there is such a direct relationship, please explain how and give a source.

I couldn't look into this too much because my real-life limitations were acting up, so all I could do is post these questions here. Thanks in advance for your consideration of these questions! Geekdiva (talk) 02:00, 13 October 2018 (UTC)

Bhinder et al journal article: Consanguinity: A blessing or menace at population level?
This journal article might be worth citing:

Average DNA shared table
Various IPs (presumably the same editor) have made multiple attempts to rewrite the Average DNA shared table in the Genetic definitions. I think it makes more sense to leave the table as is, with the relationship first and then give the average DNA shared. I assume that readers will be looking at the table to determine what the average degree of shared DNA is for a particular relationship (say between first cousins: 12.5%), rather than saying, "I wonder what relationship has 5.46875% shared DNA?" and finding that it is a "3.5-tuple-2nd cousin-pibling / 3.5-tuple-2nd cousin-nibling". I also agree with user:Craig Butz and user:Erp that we should use the common terms used in the ref and that everyone knows rather than such terms as "pibling" and "nibling".

If there are useful missing entries that need to be added to the table that's fine. Source them and add them, but let's not add such incomprehensible oddities such as "sesqui-1st great-cousin-pibling / sesqui-1st great-cousin-nibling" Meters (talk) 03:30, 26 October 2019 (UTC)

Agree that the chart should use common terminology and does not need to include every possible relationship. The goal is to help the reader understand the topic of the pages, not to introduce them to recently invented and little used words that are not the main topic of this page. Also, it makes sense for the terms to come before the percents.Craig Butz (talk) 06:39, 1 February 2020 (UTC)
 * Multiple IP blocks have not stopped this. Page protection is likely next. Meters (talk) 22:21, 4 February 2020 (UTC)
 * I've removed a lengthy talk page addition on this by yet another IP from Brazil as WP:BLOCKEVASION of .  Meters (talk) 04:13, 18 February 2020 (UTC)

"Consanguinity (in Canon Law)" listed at Redirects for discussion
An editor has identified a potential problem with the redirect Consanguinity (in Canon Law) and has thus listed it for discussion. This discussion will occur at Redirects for discussion/Log/2022 March 12 until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Veverve (talk) 13:06, 12 March 2022 (UTC)

The numbers in the chart are off
Person X's siblings, the parents of X, and the direct offspring of X all share on average 50% DNA with X, and thus they all have the same degree of consanguinity with X. The "Table of Consanguinity" displayed to illustrate the article has erred on this point, and thus many of the numbers in the chart are wrong. Compare with the CC-chart here, which is correct:.

This seems like a fundamental error, and I think that the chart should not be used without this issue being fixed. ––St.nerol (talk) 17:44, 19 April 2022 (UTC)
 * I think the table in the intro is using the legal definition (US at least).  See for instance  where "Brothers/Sisters - Half-Brothers/Half-Sisters - Grandchildren - Grandparents" are second degree.  What it does need is a proper reference. --Erp (talk) 04:00, 5 May 2022 (UTC)