9.1 How did you make out constructing a Parental Tree for 2 individuals who have a Coefficient of Relationship of 5/8? One way to approach this problem is to remember that when 2 individuals are related to each other in more than one way, their total CR is the sum of the CR’s for each relationship. Thus to get 5/8, one obvious way would be to add ½ or 4/8 to 1/8, giving 5/8. Relationships with these CR’s that spring to mind are father-son (½) and Great Grandfather-Great Grandson (1/8). And remember, I suggested than Abner and Zeke be replaced by Atlas and Zeus, who are male cattle.
9.2 As we can see in Chart 24, Atlas has an offspring with his Son’s Daughter, i.e. his Granddaughter. That offspring, Zeus, is thus his Son and his Great Grandson. 4/8 + 1/8 = 5/8. In this context BTW, Fathers are called Sires and Mothers are Dams. Such a procedure is often used in animal husbandry to “concentrate” the favorable genetic traits of a Sire, altho it can have negative side effects as a result of inbreeding, and works best when the Sire has few unfavorable recessive traits.
9.3 And just to round out the Eighths, Chart 25 gives examples of the 2 highest such CR’s. On the left, Zeus is both Son and Grandson of Atlas…2/4 + 1/4 = 3/4. And on the right, Zeus is Son, Grandson, and Great Grandson of Atlas…4/8 + 2/8 + 1/8 = 7/8.
9.4 Today’s main topic is Twins, or I should say Identical Twins, the result of a single sperm fertilizing a single egg, then that egg splitting in 2, resulting in 2 individuals that have an identical genetic make-up. They have a CR of 1. To the left is a style of headwear called a “cocked hat,” and that’s what Identical Twins knock the CR’s of their descendants into.
9.5 Well, it isn’t actually that bad…the key point is this: In figuring how closely their descendants are related to one another, Identical Twins are considered to be the same person. Now obviously, when Identical Twin Sisters have children, those children are 1st Cousins. But instead of a CR of 1/8, theirs is 1/4, or the equivalent of Half Siblings. In Chart 26, I have represented the Twins as 2 circles touching. You can see the similar “W” pattern in their Parental Tree compared to that of normal Half Siblings.
9.6 The CR’s between the descendants of Identical Twins is double what it would be for Normal Siblings, except of course the CR between Parent and Child is still ½. But the CR between one Twin and her Niece, her Twin Sister’s Daughter, is also ½. Thus, the doubling of the CR occurs between the Twins descendants, and between those descendants and the Twin Sister of the Twin they are directly descended from.
9.7 It’s important to note that the CR between Identical Twins and their ancestors remains unchanged, as does the CR between the Twins (and their descendants) and their collateral relations (and their descendants.) Collateral relations meaning other Siblings, and all Cousins. And that makes sense…to the Brother of the Twin Sisters, his Nieces are his Nieces. They may be as closely related to each other as Half Siblings, but to their Uncle, they are simply Nieces, the same as if they really were, to each other, Half Siblings or even Full Siblings. (Remember, your Half Niece is the Daughter of your Half Brother. If your Full Brother has Daughters by 2 different women, they are both your Full Nieces, altho Half Sisters to one another.)
9.8 Likewise, in Chart 27, when Identical Twins marry Identical Twins, the resulting 1st Cousins are as closely related as Full Siblings. Again, you’ll recognize the “X” pattern of Full Siblings. And I have read several accounts on the net of this happening (double wedding of course!) and indeed the 1st Cousins resembled each other as much as Full Siblings would. Which brings us to…The Patty Duke Show.
9.9 And there’s Patty, losing control…apparently there’s a hot dog nearby…or is that Cathy? Or one of each? The premise, as you recall, was that Patty and Cathy were “identical cousins.” And in one episode in the 2nd season, the idea was pushed even further, as a “distant cousin” Betsy from Chattanooga came to visit…she was “identical” too, of course, except for her accent! Now I had it my mind that this was explained by their Mothers being Identical Twins. And indeed, in the never broadcast pilot episode, Cathy and her Father, come from England to live with the Lanes in Brooklyn Heights. He’s Martin Lane’s brother, and they were played by different actors.
9.10 However, during the first season, it was established that their Fathers were Identical Twins. In fact, on an episode aired on Christmas Day (yup, no re-runs back then on holidays!) Cathy’s Father, Kenneth Lane, is played by William Schallert, who also played Martin, Patty’s Father. Now the series ran for 3 seasons, 104 episodes, and it’s indeed possible, using the forgetful logic of the TV world, that the Identical Twins in the family switched from Fathers to Mothers…or perhaps it was both.
9.11 And if it were both, that would certainly increase the chances of a pair of 1st Cousins looking very much alike, as 2 Full Siblings sometimes do. Remember, if both their parents were Identical Twins, genetically Patty and Cathy would be Full Siblings. But other than that, there is really no such thing as “Identical Cousins.” Now I say that with a caveat. When the show was made back in the 1960s, we didn’t yet have in vitro fertilization. Is it possible for a fertilized egg to split in 2 outside the womb, then the 2 embryos be implanted in 2 sisters? The resulting children would technically be 1st Cousins, the Daughters of Sisters (or at least born from 2 Sisters) altho by their genetic make-up they themselves would be Identical Twins. I’m just sayin’…
9.12 Most Twins are not Identical Twins. Fraternal Twins are as related to each other as normal Siblings, with a CR of ½. It turns out that about 2% of the word’s population are Twins of either kind…with Identical Twins making up just 8% of all Twin births. But they’ve recently discovered a third kind of twin, called Semi-Identical, Half Identical, or Polar Body Twins.
9.13 And interestingly enough, Semi-Identical Twins have a CR of 3/4…the same as those Super Sister Bees back in Part 5. The biological mechanism is similar, but not identical. Recall that with some species of Bees, a male develops from an unfertilized egg. He has just one set of genetic material, so that his sperm cells are all genetically identical to him and to each other. Thus the daughters of a male Bee share all their Father’s genes and half their Mother’s, for a CR of 1/4 + ½ = 3/4. (Remember, when we say you share half your genes with your Sibling, this is due to your sharing 1/4 of your Father’s and 1/4 of your Mother’s genes with that Sibling…Full Siblings are essentially Double Half Siblings.) And of course, only female Bees can be Super Sisters..there are no other types of Bee Super Siblings, due to the unique genetic make-up of the males.
9.14 With humans, Semi-Identical Twins are slightly different, as seen here in Chart 28. The exact mechanism for the production of Semi-Identical Twins is not well understood, but to simplify…it involves 2 different sperm cells fertilizing one single egg. Either literally, as show in the Chart 28, or an egg fertilized by a single sperm cell begins developing, and one of the normally discarded products of this development, called a polar body, is fertilized by a different sperm cell. This happens early enough in the development of the embryo that the polar body is apparently fully capable of developing into a fetus…in some case, with various abnormalities, including hermaphroditic features…altho in other cases, the Semi-Identical Twins, both males or both females, are perfectly normal.
9.15 Now it would be impossible to know any of this without DNA analysis…and in fact, whether Twins are truly Identical or merely Fraternal has always been a matter of “eyeballing” them. For example, you might hear it said that Elvis Presley’s stillborn brother Jesse was his Identical Twin. How they could have known that is anyone’s guess. Oh, the Mother always knows… Well, as a matter of fact, it’s the Mother and all the other close family members who see how different Identical Twins really are…and there are some borderline cases where the family says Fraternal, while the rest of the world thinks Identical. The Olsen Twins, Mary-Kate and Ashley, are a perfect example. They are always described by their family as Fraternal, despite how closely they seem to resemble each other. Could they be…perhaps…Semi-Identical?
9.16 Next week, we’ll “remove the Removeds”…and I’ll answer some readers’ questions. Till then…We’re gonna need more Tinker Toys!
I was flattered to find out that some people didn’t realize these are all my original Charts…well, the concepts behind them aren’t original, but I do “draw” the charts myself, trying to find the best way to illustrate those concepts. Here’s a case in point…Octuple Half 2nd Cousins…yup, Abner and Zeke are Half 2nd Cousins 8 different ways…for an ultimate CR of 1/8, or the equivalent of Full 1st Cousins. The chart is based on one at this website, which goes into this stuff far deeper than I do, if you’re game… Quantitative Genealogy from the UK .
Copyright © 2011 Mark John Astolfi, All Rights Reserved
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