Flaw in Melungeon DNA Test

             Flaw in Melungeon DNA Test
             This blog post is in responce to the Huffington Post article found here.

http://www.huffingtonpost.com/2012/05/24/melungeon-dna-study-origin_n_1544489.html#postComment
I have taken an autosomal DNA test and it came back mostly Caucasian, but we do have some American Indian and some sub-Sahara African DNA as well. Our triracial identity is confirmed. My ancestors were NOT a part of that study, however we lived there, on Copper Creek, Scott Co., Va just like they did and we attended "Stoney Creek Primitive Baptist Church" just like known Melungeon families did, and our closest neighbors were Gibsons descended from a known Melungeon family. My response to that article is below.
 Assume 30 American Indians, full blood, 15 male, 15 female. They are surrounded by 80 percent  Caucasians, and 20 percent African Americans. Assume 20 percent of the American Indians marry others with Indian blood.  Of the remaining 80 percent, 60 percent marry a Caucasian and 20 percent marry an African American. How many generations will it take for people of straight male or straight female line of American Indian descend to disappear?

These will be recorded (m,f) by race. 30 Indians. First generation – 20 % of 30 is (0.2)*30= 6 of these 30 marry other American Indians. These families would be (I,I), (I,I), (I,I) leaving 24 American Indians. SIxty percent of these 30 marry Caucasians, and 20 percent of these 30 marry African Americans. 60% of 30 is (0.6)*30= 18 Indians marrying Caucasians. 20% of 30 is (0.2)*30= 6 American Indians marry African Americans. Assume half male and half female. After one generation we have the following unions.

If we consider the first variable to be male and the second female, which can be represented as (m, f), and replace M and f with the race of th individual as W (Caucasian), B (African), and I (American Indian), we have the following. If we are interested in the American Indian component, we have;

(I,I), (I,I), (I,I) ó (3,3) ó (3 Indian males, 3 American Indian females)

(I,W), (I,W), (I,W), (I,W), (I,W), (I,W), (I,W), (I,W), (I,W)  ó (9,0) ó (9 American Indian males)

(W, I), (W, I), (W,I), (W,I), (W,I), (W,I), (W,I), (W,I), (W,I) ó (0,9) ó (9 American Indian females)

(I, B), (I,B), (I,B) ó (3,0) ó (3 American Indian males)

(B, I), (B, I), (B, I) ó (0, 3) ó (3 American Indian females)

Of the original 30, only 15 have Indian blood on the father’s side for 2 generations, and only 15 have females on 2 generations of the female side. It is important to know that while there is NO new infusion of American Indian blood, yet the infusion of both Caucasian and African blood is inexhaustible.

We can extrapolate that since after only one generation of mixing race, only 50% of the original American Indian y-chromosome is left, that 50% will be lost also in each generation. Likewise, only 50% of the mtDNA, which we inherit from our mothers, will remain from the American Indian side of the lineage. So we can extrapolate further generations –

RETENTION OF AMERICAN INDIAN Y-CHROMOSOME DNA

1^st generation – 100%

2^nd generation – 50 %

3^rd generation – 25%

4^th generation – 12.5%

5^th generation – 6.125%

6^th generation – 3.0625%

In the year 1800 these families were considered mixed-bloods. If we consider 4 generations per century, by the year 2000 we have 8 generations passing since the year 1800. So let’s add 2 more generations.

7^th generation – 1.53125%

8^th generation – 0.765625%

Oh yes, don’t  forgot, these people were already mixed when they were first recorded about the year 1800, so let us add one more generation:

9^th generation – 0.3828125, or slightly more than one third of one percent of the descendants of the original 30 American Indians would still retain the American Indian markers of their y-chromosonal DNA, or the mtDNA markers from an American Indian ancestor. To determine a value we might expect from these original 30 Indians, just multiply (number of American Indians) by the probability that their Y-chromosome or mtDNA is preserved, and after 9 generations we get (30 persons)* (0.3828125)= 1.14843750, or about one of those original 30 might still retain that original information. And lo and behold, look at the Sizemore surname, it DOES retain the Y-chromosome DNA marker of an Indian ancestor. The laws of Probability Theory don’t lie. Conversely, if there is one marker that exists from an isolated community, there could be another thirty families that have lost that marker. And that is exactly what we have.

The key to understand this decline is the limited numbers of American Indians. While each generation there is a new infusion of Caucasian and sub-Sahara African DNA, the American Indian DNA was from a few original donors, only. Through the generations, there was never a new infusion of those markers, so they continued to decline, generation after generation.