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4 votes (18.18%)
18 votes (81.81%)

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Wizard
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Wizard
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April 8th, 2011 at 2:55:04 PM permalink
Here is a way to think of it. Suppose 40 numbers, instead of the usual 20, are drawn in keno. For those who don't know, a keno hopper has 80 balls. The keno hopper represents the combined gene pool of both parents.

The draw of 40 balls are the genes given to any one child.

So in two draws the number of balls drawn common to both draws would be 20. So two children would have 20 genes in common, or half of them.
It's not whether you win or lose; it's whether or not you had a good bet.
pacomartin
pacomartin
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April 9th, 2011 at 6:31:08 PM permalink
Normal first cousins share 1/8 of their genes inherited from a common ancestor. By "normal" I mean they are not "half first cousins" or "double first cousins".

Should these first cousins produce a child that child will have a coefficient of inbreeding (F) of F = 0.0625 or 1/2 *1/8 = 1/16.
That is, the progeny are predicted to have inherited identical gene copies from each parent at 6.25% of all gene loci, over and above the baseline level of homozygosity in the general population.

Typical inbreeding percentages are as follows, assuming no previous inbreeding between any other ancestors :
Father/daughter, mother/son or brother/sister → 25%
Half-brother/half-sister → 12.5%
Uncle/niece or aunt/nephew → 12.5%
Half-uncle/niece or half-aunt/nephew → 6.25%
First cousins → 6.25%
First cousins once removed or half-first cousins → 3.125%
Second cousins or first cousins twice removed → 1.5625%
Second cousins once removed or half-second cousins → 0.78125%
Third cousins → 0.39063%



For instance Prince Charles parents are both (a) 2nd cousins once removed by descent from the King of Denmark who died in 1906, and (b)3rd cousins by descent from Queen Victoria and Prince Albert. That would imply his consanquinity index is 0.78125%+0.39063%. However Queen Victoria and Prince Albert were also first cousins. Adding up all the relationships in his family Prince Charles has a Consanguinity Index=2.07%. His great great grandfather Edward VII, King of the United, Kingdom who was the child of Queen Victoria and Prince Albert had a Consanguinity Index=8.03%.

British citizens of Pakistani descent have 55% of all marriages between first cousins. Being a child of a first cousin marriage results in F=6.25%, but if you add in previous generations the number keep going up. Pakistani children in UK have high percentage of genetic diseases . Around 50% of children born in Bradford are to Pakistani parents. Since 1997 there have been 902 British children born with neurodegenerative conditions and 8% of those were in Bradford which only has 1% of the population. If your parents are first cousins, and both your grandparents and great grandparents are first cousin marriages your F=9.375% which is starting to get into the range of being a child of an uncle/niece marriage.

The most famous of the inbred royals in Europe was, Charles II, "The Hexed" the last of Spanish Hapsburg royals. He had an almost endless list of disgusting problems because of his genetic inbreeding. Modern geneticists going back 14 generations have calculated his F=25% (the same as if he had been to full blooded brother and sister). The coefficient was so high because of numerous cousin marriages and several uncle/niece marriages in his ancestry. His death in 1700 started the War of the Spanish Succession (the first global conflict), followed by the Napoleanic Wars and WWI and WWII.



Once you get to 4th cousins and beyond there is no way to genetically detect the relationship. So while Prince Charles and Lady Diana were 7th cousins once removed (and dozens of other more remote relationships), Prince William has a very low consanguinity index as he must trace his family tree back at least 6 generations until the same people begin to appear more than once.
Doc
Doc
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April 10th, 2011 at 6:21:23 AM permalink
I'm coming a little late to this discussion and haven't re-read the thread, so maybe I missed something....
Quote: Wizard

Here is a way to think of it. Suppose 40 numbers, instead of the usual 20, are drawn in keno. For those who don't know, a keno hopper has 80 balls. The keno hopper represents the combined gene pool of both parents.

The draw of 40 balls are the genes given to any one child.

So in two draws the number of balls drawn common to both draws would be 20. So two children would have 20 genes in common, or half of them.


Wizard, I'm a bit confused about your analogy of selecting 40 of the 80 keno balls representing "the combined gene pool of both parents." Are you suggesting that one child (or both) might possibly have the exact same 40 "genes" as one parent and none of the "genes" of the other parent? That sounds more like cloning than the usual genetics. Seems to me the analogy would need to involve draws from two different keno hoppers, like a modified PowerBall.
BioProf
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April 27th, 2011 at 1:12:04 PM permalink
Mike, I think you are quite wrong on this one. Humans have 23 pairs of chromosomes, one from the mother and one from the father. Imagine TWO Keno hoppers. Each one has 46 balls, two each for #1-23. One hopper normally has a complete set (#1-23) of blue balls and a complete set of red balls. The other has a set of teal balls and a set of pink balls.

When a sperm or an egg is made, one member of each set, either a blue or a red or either a teal or a pink, is RANDOMLY put into the sperm or egg. So, the odds of any two sperms or any two eggs having the same chromosomes is 1/2 x 1/2.... twenty three times. Or really, really big odds. Now, the odds two sperms that are the same fertilize two eggs that are the same is one really, really big number squared. Basically, it is next to impossible that any two offspring of the same two human parents have the same genetic make-up. And it is likewise next to impossible to answer HotBlonde's question.

And all of the above completely ignores the phenomenon of crossing-over which guarantees that the genes on any pair of chromosomes are randomly mixed up every time a sperm or egg is made. This guarantees human uniqueness. And it means you can't even come up with a true average to answer HotBlonde.

But, this all being said, as a retired biology professor, I would suggest that HotBlonde should still probably avoid sexual relations with the sibling. It just seems a bit icky, though there really is no biological reason to do so as long as it has not been done by HotBlonde's previous generations.
Doc
Doc
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April 27th, 2011 at 4:54:39 PM permalink
I am most definitely not a retired biology professor -- I have only taken one biology course in my life, in high school, and I didn't pay much attention then. That's my excuse for describing my suggested two-keno-hopper analogy as "modified PowerBall". I didn't know any better, so I defer to those who know what they are talking about.

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