Talk:Coefficient of relationship

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Step siblings are missing from the diagram[edit]

Step siblings are much closer than many of the relatives shown in the diagram, but step siblings are omitted. — Preceding unsigned comment added by (talk) 06:55, 26 May 2015 (UTC)

Moved from main article[edit]

== Sexual organisms ==
=== Parent-offspring ===
For a sexual organism, the coefficient is 0.5.
== Haplodiploidy ==
In haplodiploidy, things get screwed around a bit.
== Philandering ==
being naughty reduces the coefficient.
== Sex chromosomes ==
Sex chromosomes reduce the relatedness slightly 
== Finite populations ==
Finite and small population size mean that it can be negative.  hence spite.

It was already commented out, so I put it somewhere more public. Anyone want to fix this? alerante  20:55, 9 September 2005 (UTC)

Wording updates needed[edit]

The article addresses the reader directly, for example by posing questions, which WP:TONE says is inappropriate tone for an article. Can someone take a crack at re-writing these sections to use a better tone? --ΨΦorg (talk) 22:27, 6 October 2008 (UTC)

I am a person with a background in biology and biochem, am (obviously) good at math, have a basic understanding of genetics, and am a writer to boot. That being said, I cannot understand what this writer is trying to say. My opinion is that some people are very knowledgeable in their subject area, but make terrible teachers. No matter how hard they try, they simply can't explain something to another person using plain, easily-understood English. Others are very gifted in the art of 'splainin' (Carl Sagan: astronomy; Bill Clinton: politics). This writer belongs to the former group, unfortunately. I was left shaking my head with confusion, due almost exclusively to the wording.

Two examples from the text.

"Each such line connects the two individuals via a common ancestor, passing through no individual who is not a common ancestor more than once."


In trying to understand the latter half of this sentence, I jumped through the following logic:

  • If two people share a 'common ancestor,' then that person appears in the family tree of both people.
  • A person who is a 'common ancestor more than once' is someone who appears in the shared family tree in two or more places.
  • A person who is 'NOT a common ancestor more than once' appears in the shared family tree of both people only ONCE.
  • '...passing through NO INDIVIDUAL who is NOT a common ancestor more than once' means passing through NO SHARED ANCESTOR WHO APPEARS ONCE ONCE.

Thus, the line must pass through a common ancestor two or more times. Is this what the writer intended? I don't think so, because first cousins share only a grandparent. Once. This is as clear as mud.

"...where p enumerates all paths connecting B and C with unique common ancestors (i.e. all paths terminate at a common ancestor and may not pass through a common ancestor to a common ancestor's ancestor)..."

First, by definition, a 'common ancestor' is not a person who is unique. So, what is a "unique common ancestor"?

And does the writer simply mean that a path should be traced back to the first ancestor that is common to both people, and that it should STOP THERE? If so, say this.

This wording is just unbelievably poor! There are other small grammar corrections I would probably make ("To given an artificial example"; "fewer generations," not "less generations"; etc.), but I'd start with easy-to-follow wording and a real-life example or two--worked start to finish.

IMHO, this is the kind of article that makes people hate science and math.

Mrs rockefeller (talk) 22:53, 12 April 2015 (UTC)

Not numerology[edit]

Someone acting under the cover of a bare IP number categorized the article as "Numerology". I have reverted this as it isn't numerology, but describes a useful quantity that connects to scientific theories. Felsenst (talk) 12:01, 17 July 2010 (UTC)

Coefficients incorporating incestuous ancestry?[edit]

Has it been calculated what effect previous incestuous relationships in the parents' ancestries have?

E. g., how would 'r' increase for two first cousins where one is already the result of such relationship and the other has a parent who is also such a result? -- (talk) 22:22, 6 October 2011 (UTC)

2 x the coefficient of inbreeding?[edit]

The coefficient of inbreeding of who? One individual? Perhaps you meant the coefficient of kinship of a random copy of the gene in one individual with a random copy of the gene in the other? Felsenst (talk) 12:28, 25 October 2011 (UTC)

The second sentence of the page is

The 'Coefficient of Relatedness' (or: coefficient of kinship) is defined as the probability that the alleles at a particular locus chosen at random from two individuals are identical by descent.

This is totally unclear. The coefficient of kinship between individuals A and B is the probability that a random one of the two copies from A is identical by descent to a random one of the two copies chosen from individual B. That is also the inbreeding coefficient of the offspring that would result from mating individual A and individual B. (Although we can calculate the coefficient of kinship even for two indviduals who cannot be mated, as when they are of the same sex). The coefficient of relationship used in (say) kin selection calculations is different. Felsenst (talk) 15:29, 26 October 2011 (UTC)

Well, the case is much more complicated than this article suggests. These coefficients were defined for use in actual breeding (of animals, I should say, even though they are now also used to examine human genealogies). Their definition is correspondingly complicated. To calculate the coefficient, you would need to know the complete family tree of the two individuals down to all of their common ancestors. This is usually the case in breeding situations, where you start with a given ancestor population and then keep accurate records of each pairing, but it is clearly impossible in most human scenarios. The point is that if the number of generations separating the two individuals from their common ancestors increases, the coefficient approaches zero.

So, the "dumbed down" definition of this coefficient is that you assume that all common ancestors except the ones under explicit consideration are assumed to be arbitrarily far removed. In this case, you get the simple powers-of-two rules of "siblings 2^-1, cousins 2^-3, second cousins 2^-5" etc. But obviously this article should give the full definition, and then treat the simplified "cousins table" as a special case. --dab (𒁳) 15:03, 5 January 2012 (UTC)

ok, I should admit that I am struggling here, as I am reading up on this definition for the first time. Help is appreciated. What is clear is that the article was completely mistaken. The coefficient isn't even defined in terms of genetics, but in terms of genealogy. It can be calculated precisely if the full genealogy is known, never mind genetics. Of course it is intended to still make a statement about genetic relatedness, but that's not part of its strict definition. It is intended to describe breeding processes of mammals, so I am not sure it can even be meaningfully applied to hymenoptera genealogies. I have so far looked up the 1922 definition of r. It involves summing over all paths in the full genealogy. The thing being summed are path coefficients, and these path coefficients are in turn defined in terms of the inbreeding coefficient. As the inbreeding coefficient isn't defined in the 1922 paper, the reader just being referred to the 1921 one, I have not so far been able to supply the full definition. --dab (𒁳) 15:30, 5 January 2012 (UTC)

Title of article[edit]

The phrase "coefficient of inbreeding" shows up in Google results over 5 million times, while "coefficient of relationship" shows up only 3.5 million times. Since "coefficient of inbreeding" is by far the more commonly used phrase, shouldn't that be the article's title (with "coefficient of relationship" redirecting to it? (talk) 15:17, 22 October 2014 (UTC)

Well I don't think this article has anything to do specifically with inbreeding. Only if the people with high Coefficients of relationship started copulating would if have anything to do with inbreeding. Perhaps a "See also." Cloudswrest (talk) 17:07, 22 October 2014 (UTC)

Double first cousins[edit]

In what way is marriage between double first cousins a "rare case"? There are cultures where it is quite common, driven by a combination of arranged marriages and a dowry culture where the large dowry one family is expected to provide but cannot is offset by the expectation of an equal and opposite dowry going the other way. Philip Trueman (talk) 17:07, 22 December 2014 (UTC)

Degree of relation[edit]

Why is uncle-neice listed as a 3rd degree relationship? This is a 2nd degree relationship ... (talk) 21:48, 13 February 2015 (UTC)

I believe it is the minimum number of links on the graph connecting two people, niece -> parent -> grandparent -> uncle. Three links. Cloudswrest (talk) 22:31, 13 February 2015 (UTC)