Talk:Double first cousin

message: What if two random persons, albeit the improbability of so occuring, share all of their great great great grandparents but none of their great great grandparents? (As in double cousins who share all of their grandparents but none of their parents) What would their consanguinity be? Is there a way to calculate this? 
Elsewhere in wikipedia it is said that if any two people taken at random are not siblings, cousins (first, second or third, an undefined but posibly finite number of times removed at most) or ancestors-descendant their consanguinity is genetically the equivalent (not necessarily the same) as if they were fourth cousins. But in this case they are {doub[to the x]}le fourth cousins and if double cousins are taken as full siblings, half siblings or something in between depending on their twinness or lack thereoff these would certainly have a closer relationship, yet, not as close as that of full or even half siblings... Would they? If X generations behind all ancestors are the same but X-1 generations behind all ancestors are different (with an algorithm, if possible, to determine this as identical, non-identical twins occur more and less in numbers), which value must X have so their consanguinity is, as exactly as it can be, the equivalent to that of fourth cousins? (I know the question might be bizarre, but it would illustrate better the genetics and genealogy of inheritance to the uninitiated) Undead Herle King (talk) 15:25, 27 March 2008 (UTC)
thread_title: Consanguinity, algo'rhythm and the fourth cousins rules

message: What happens if two men who are brothers marry two women who are cousins? I had some friends whose fathers married women who were second cousins (IIRC). The children were not double first cousins, but they were both first and third cousins. Is there a technical term for this? 169.199.113.163 02:38, 18 July 2007 (UTC)
replies: text: No, there is not a technical term for this. Most often, the closest relationship would be used. In this instance, it would be first cousins. Charles 04:32, 18 July 2007 (UTC)
thread_title: Siblings marrying cousins

message: What would happen if two female first cousins married two male second cousins.If both couples have children what would the relation be between the children. —Preceding unsigned comment added by 67.80.106.105 (talk • contribs) 
:The children would be double second cousins of one another, since they would have two sets of great-grandparents in common rather than one. Charles 00:56, 2 February 2008 (UTC)
replies: text: The children would be maternal second cousins & paternal third cousins. GoodDay (talk) 02:51, 2 February 2008 (UTC)
replies: text: Ooh, I missed the "second" in the latter. Thank you for catching that! GoodDay is correct. However, in terms of describing genealogical relationships, the closest one is used. In practice, the order of precedence is relationships of descent, ones of varying degrees of aunt/uncle/niece/nephew and finally those of just cousins, with the closest relationship being used. The children of these first cousin wives and second cousin husbands would more often than not be described as second cousins to one another. Charles 03:21, 2 February 2008 (UTC)
thread_title: Two sets of cousins marry two other sets of cousins 

message: Can anyone provide a citation for this?  I haven't been able to find a site yet that actually shows how the coefficient is calculated.  However, from what I can find - the dictionary definition - the figures in the article are wrong.  The definition is "the probability that two homogenous genes from two different people came from the same ancestor".   For first cousins, that probabilty is 1/8.  Let GP1 and GP2 be the first cousin's non-shared grandparents, GP3 and GP4 the second cousin's non-shared grandparents, and GP5 and GP6 the shared grandparents.   The possible genetic sources are then:
GP1 and GP3, GP1 and GP4, GP1 and GP5, GP1 and GP6
GP2 and GP3, GP2 and GP4, GP2 and GP5, GP2 and GP6
GP5 and GP3, GP5 and GP4, GP5 and GP5, GP5 and GP6
GP6 and GP3, GP6 and GP4, GP6 and GP5, GP6 and GP6
As you can see, out of the 16 possible combinations, 2 of them result in a match.  2/16 = 1/8 = 0.125.
Similarly, half-siblings and double-first cousins are both 1/4.  Siblings and double-first-cousins of identical twins are both 1/2.
If I've made a mistake in this mathetmatics, please provide a reference that instructs how the coefficient of coancestry is calculated.
MrItty (talk) 19:16, 10 June 2008 (UTC)
thread_title:  Citation for calculation of coancestry coefficient? 

message: There are six people. Persons A, B, C, D, E, F. Persons A, C, and E are full siblings. Persons A and B marry and have a child: person G. Persons C and D marry and have two children: persons H and I. Persons E and F marry and have a child: person J. Persons G and H marry and have a child: person K. Persons I and J marry and have a child: person L. Persons K and L marry and have a child: Person M. What is the degree of consanguinity between persons K and L? What is the coefficient of inbreeding of person M?
In another case, there are four people. Persons 1, 2, 3, 4. Persons 1 and 3 are full siblings. Persons 1 and 2 marry and have two children: persons 5 and 6. Persons 3 and 4 marry and have two children: persons 7 and 8. Persons 5 and 7 marry and have a child: person 9. Persons 6 and 8 marry and have a child: person 10.  Persons 9 and 10 marry and have a child: person 11. What is the degree of consanguinity between persons 9 and 10? What is the coefficient of inbreeding of person 11?  — Preceding unsigned comment added by 188.221.174.97 (talk) 03:13, 4 September 2016 (UTC)
thread_title:  Calculating inbreeding coefficient?