20 February 2016

X-Chromosome: The X-tra Special Chromosome

By Emily Aulicino for the Genealogical Forum of Oregon (GFO) Bulletin

What makes the X-chromosome so special? Mainly it is a pattern of inheritance. Like the other twenty-two chromosomes, it randomly recombines in meiosis, but unlike the other twenty-two, only certain ancestors are contributors. Furthermore, males and females inherit differently.

The X-chromosome is one of the two sex chromosomes, and it helps determine gender. A female receives two X-chromosomes, one from her father and one from her mother. A male has only one X-chromosome, which he receives from his mother. At conception (actually at meiosis), a mother’s two X-chromosomes go through a recombination process, thus scrambling segments on the two chromosomes and even moving some segments from one chromosome to the other. The mother gives one of the randomly recombined X-chromosomes to her child (son or daughter), but each child receives a different randomly-recombined X-chromosome. Fathers, however, have only one X-chromosome that is passed only to their daughters without going through the recombination process. Fathers do not give an X-chromosome to their sons because they give them the Y-chromosome.

However, the father’s X-chromosome is a random mix of his parents and of his ancestors who were able to contribute to this chromosome.

Due to the way the X-chromosome is passed to the next generation, the inheritance of it varies between the genders and only specific ancestors can contribute. Naturally, as females get two X-chromosomes, they receive more matches than males, and because males receive their X from their mothers, their matches will be only on their mother’s half of their pedigree chart. As it can be difficult to visualize the route of inheritance for each gender, using the appropriate list of numbers (figure 1) from an ahnentafel chart or completing the fan chart created by Dr. Blaine Bettinger (figure 2) is quite helpful. The percentages in parenthesis after the numbers in the second table (figure 1) are the estimated average amounts contributed by that ancestor for the male inheritance. Due to recombination from a mother’s X-chromosomes, actual percentages cannot be confidently provided.

With recombination, it is unlikely that a female will receive 50 percent of her X-chromosome from her moth­er’s father and 50 percent from her mother’s mother. It is more likely to be a far different percentage anywhere from 0 percent to 100 percent for either of the parents. This means any ancestor can be over or under repre­sented in the X-chromosome, according to Dr. Bettinger, the Genetic Genealogist (http://www.thegeneticgene­alogist.com/2009/01/12/more-x-chromosome-charts/). For this reason, one should not assume that finding the common ancestor for a match will be easy. However, you can more easily determine who may have contributed a segment of the X-chromosome by using the tables (See Figure 1) or by using the fan charts prepared by Dr. Blaine Bettinger (See Figure 2). Remember to use the correct one for your gender.





                        Figure 1 from Genetic Genealogy: The Basics and Beyond, p. 43


31 (12.5%)
109 (12.5%)
213 (12.5%)
238 (3.125%)
3 (100%)
53 (25%)
110 (6.25%)
214 (6.25%)
239 (3.125%)
6 (50%)
54 (12.5%)
111 (6.25%)
215 (6.25%)
245 (6.25%)
7 (50%)
55 (12.5%)
117 (12.5%)
218 (6.25%)
246 (3.125%)
13 (50%)
58 (12.5%)
118 (6.25%)
219 (6.25%)
247 (3.125%)
14 (25%)
59 (12.5%)
119 (6.25%)
221 (6.25%)
250 3.125%)
15 (25%)
61 (12.5%)
122 (6.25%)
222 (3.125%)
251 (3.125%)
26 (25%)
62 (6.25%)
123 (6.25%)
223 (3.125%)
253 (1.5625%)
27 (25%)
63 (6.25%)
125 (6.25%)
234 (6.25%)
254 (1.5625%)
29 (25%)
106 (12.5%)
126 (3.125%)
235 (6.25%)
255 (1.5625%)
30 (12.5%)
107 (12.5%)
127 (3.125%)
237 (6.25%)

                             Figure 2 from Genetic Genealogy: The Basics and Beyond, p. 43

Figures 3 and 4 Courtesy of Blaine Bettinger, Ph.D.

Although the X-chromosome and the autosomal DNA are sequenced at the same time, only Family Tree DNA and 23andMe (of the three major testing companies) al­low you to view your X-chromosome matches directly at their website with a chromosome browser feature. With AncestryDNA, you must download your autosomal DNA results into GEDmatch.com to view the X-chromosome results.

The Family Tree DNA chromosome browser offers the option of viewing your results by name and several other categories, including X matches. This allows you to see only those matches with whom you share the X-chro­mosome. If more than one person appears with the same segment, email them to determine if everyone matches everyone else. This can help females determine if the match is on one X-chromosome versus the other. Males do not have to compare their matches with each other to determine which side of their family has the match, as they only inherit their mother’s X-chromosome.

Because the X-chromosome is inherited differently be­tween the genders, and because not every ancestor has the possibility of contributing to the X-chromosome, it is important to create an X-chromosome ahnentafel to help you focus on the ancestral lines to assist in finding the common ancestor.

Using your genealogy software, create an ahnentafel chart, and then delete all the numbered ancestors that do not correspond to the table for your gender. When gen­erating a list for how the X-chromosome is inherited, a male starts with his mother and a female starts with herself. Keep this ahnentafel in a document you can share with your matches. (See Figure 5.)

The following is only five generations of my ahnen­tafel chart for the X-chromosome, but I offer all I have on my ancestors to my match. Notice that the following numbers are omitted as I do not inherit information on the X-chromosome for these ancestors: 4, 8, 9, 16, 17, 18, 19, 20, 24, 25 and so on. I tend to leave the data for each ancestor who is deceased in case location could be a factor. I also retain the children of the ancestors in hopes that my match recognizes someone. If I do not know an ancestor for a particular number, I list the person as in this example:  90. UNKNOWN father of Elizabeth Pryor who m.Daniel Simpson

for X Chromosome Matches
1. Emily Doolin

2. Donald Doolin
    3. Beverly Williams

5. Georgia Faye Williams, born 25 Mar 1898 in Waynesville, Pulaski Co, MO; died 03 Jan 1980 in Kansas City, Wyandotte Co, KS. She was the daughter of 10. Benjamin Franklin Williams and 11. Tina May Simpson.
6. Clyde Mills Williams, born 22 Nov 1887 in Fort Scott, Bourbon Co, KS; died 08 Aug 1957 in Fort Scott, Bourbon Co, KS. He was the son of 12. John Joseph Williams and 13. Urvilla Victoria McCoon. He married 7. Emily Helen Gilmore 09 Jun 1921 in Olathe, Johnson Co, KS.
7. Emily Helen Gilmore, born 14 Dec 1890 in Grays Harbor, Grays Harbor Co, WA; died 31 Aug 1942 in Fort Scott, Bourbon Co, KS. She was the daughter of 14. Lowry Graham Gilmore and 15. Mary Adeline Ogan.

10. Benjamin Franklin Williams, born 22 May 1875 in Cooper Hill, Osage Co, MO; died 05 Nov 1952 in near Waynesville, Pulaski Co, MO. He was the son of 20. Henry Jefferson Williams and 21. Syrena Simpson. He married 11. Tina May Simpson 06 Feb 1896 in Dixon, Pulaski Co, MO.
11. Tina May Simpson, born 12 Aug 1879 in Waynesville, Pulaski Co, MO; died 13 Mar 1968 in Kansas City, Wyandotte Co, KS. She was the daughter of 22. James E. Simpson and 23. Nancy Williams.
13. Urvilla Victoria McCoon, born 09 Jun 1854 in Dane Co, WI; died 09 Sep 1890 in Fort Scott, Bourbon Co, KS. She was the daughter of 26. George Henry McCoon and 27. Laura Almeda Parker.
14. Lowry Graham Gilmore, born 14 Jun 1855 in Rochester, Monroe Co, NY; died 16 Mar 1934 in Winfield, Cowley Co, KS. He was the son of 28. Robert Grey Gilmore and 29. Helen Storrier. He married 15. Mary Adeline Ogan 06 Mar 1887 in Montrose, Henry Co, MO.
15. Mary Adeline Ogan, born 11 Aug 1866 in Bureau Co, IL; died 27 Oct 1935 in Fort Scott, Bourbon Co, KS. She was the daughter of 30. Simon Peter Ogan and 31. Emily Jane Studyvin.

21. Syrena Simpson, born 06 Mar 1843 in Cooper Hill, Osage Co, MO; died 05 Jan 1919 in Bland, Gasconade Co, MO. She was the daughter of 42. James Simpson and 43. Rebecca Syrene Miller.
22. James E. Simpson, born 03 May 1849 in pos. Bates Co, MO; died 29 Mar 1924 in Helm, Pulaski Co, MO. He was the son of 44. Daniel Simpson and 45. Elizabeth Pryor. He married 23. Nancy Williams ca 1869.
23. Nancy Williams, born 1849 in IL; died Bet. 1880 - 1910 in MO.
26. George Henry McCoon, born 19 Jul 1828 in Catskill, Green Co, NY or MA; died 10 Mar 1917 in Berkeley, Alameda Co, CA. He was the son of 52. James Timothy McCoon and 53. Olive Miller. He married 27. Laura Almeda Parker 18 Feb 1853 in Albion, Dane Co, WI.
27. Laura Almeda Parker, born 1834 in NY. She was the daughter of 54. Simon Parker and 55. Lauran Unknown.
29. Helen Storrier, born 28 Apr 1812 in Dundee, County Angus, Scotland; died 22 Dec 1891 in Fredonia, Wilson Co, KS. She was the daughter of 58. David Storrier and 59. Margaret Lyall.
30. Simon Peter Ogan, born 24 Aug 1826 in Columbus, Franklin Co, OH; died 23 May 1912 in Bear Creek Twp, Henry Co, MO. He was the son of 60. Evan Ogan and 61. Susan Wical. He married 31. Emily Jane Studyvin 25 Jan 1855 in Dover, Bureau Co, IL.
31. Emily Jane Studyvin, born Apr 1836 in Dover Twp, Bureau Co, IL; died 14 Nov 1912 in Henry Co, MO. She was the daughter of 62. Madison Studyvin and 63. Frances Ellis.

To use the fan charts in Figure 3 and 4, simply photocopy the appropriate chart large enough to enter the names of your ancestors. I usually copy each fan chart on two 8 x 11 inches pages and tape them together. Having both versions (male and female) handy allows you to com­plete a sample for yourself and for a match. If you are not familiar with a fan chart, it is just a different form of a pedigree chart. The tester is number one on the chart (the center circle). Then starting on the row above the circle and to the far left, enter the parent’s name that would fit in the colored box, blue for males and pink for females. After finishing each row, go to the next row above it and to the far left again and repeat the process for your grandparents, etc. Have your X-chromosome match follow the same procedure.

For a copy of both fan charts, see: http://www. thegeneticgenealogist.com/2008/12/21/unlock­ing-the-genealogical-secrets-of-the-x-chromosome/  
http://www.thegeneticgenealogist.com/2009/01/12/ more-x-chromosome-charts/  

A variation of these charts can be seen at: http:// freepages.genealogy.rootsweb.ancestry.com/~hulse­berg/DNA/xinheritance.html  

It would seem that the process of viewing who can contribute to the X-chromosome would easily provide you with the name of your common ancestor, and in some cases it does. However, many of the matches re­ceived on the X-chromosome are not large enough to ensure success. That is, due to recombination, a great number of those matches will not share enough centi­morgans (“cMs”) to discover the common ancestor. The segments look bigger on a chromosome browser graphic than they do in the table that provides the centimorgans; therefore, view the information in the table or download it into a spreadsheet. Algorithms for the X-chromosome are not as accurate as those which determine the match­es on our other chromosomes. For these reasons focus on segments that are quite large, perhaps above 20 cMs, at least. For example, I currently have 239 matches on my X-chromosome with only three matches above 20 cMs. Smaller matches could be IBS (Identical By State1) so work with substantial segments.

My cousin Rebecca and I match several places on our chromosomes as well as on two segments of the X-chro­mosome. The largest segment is 39.54 cMs. I used Dr. Bettinger’s fan chart to determine our common ancestor. Although I knew Rebecca was a cousin on my mother’s line, I did not know which ancestor provided that seg­ment of our X until we completed the charts. As you can see from the charts below, the only name which is the same for both of us is Mary. This portion of our X came from her, but no doubt this segment has some elements of several of her ancestors. We can be certain that this portion of the X did not come from Mary’s husband Lowry as Lowry could not have given his X to his son Robert, the grandfather of Rebecca.

Example of using Dr. Bettinger’s fan chart to find the common ancestor between author and her cousin.

In comparing lineages with another match who shares 24.33 cMs, our common ancestor cannot be de­termined for several possible reasons. Knowing these reasons may help you understand why finding common ancestors can be difficult.

1. She does not know some of her X-chromosome ancestors.
2. I do not know some of my X-chromosome ancestors
3. The common ancestor’s segment could be under- or over-represented.2
4. Her lines go back to Hungary (now Slovakia) and Germany, very recently, and mine do not.
5. We do not know all the siblings of our ancestors who could have inherited this portion of the X-chromosome; therefore, it may be difficult to trace the lineage to the common ancestor.

It bears repeating that the X-chromosome is one of the two sex chromosomes. Females receive one X from each of their parents, but males only receive the X from their mothers. The X-chromosome recombines in meiosis as do the other twenty-two chromosome, and is inherited differently by men and women. Use either the table, or Dr. Bettinger’s fan charts, to create an X-chromosome ahnentafel chart to determine which ancestors could have contributed to your X. Focus on twenty centimor­gans or more for locating common ancestors.

1.       Identical by State (IBS) ― a half-identical region (HIR) in the DNA that is a small segment of DNA that came from a very dis­tant ancestor. The smaller the segment, the less likely it is to be cut by a crossover in passing to the next generation. This means that these small segments generally get passed along whole or not at all. There is a chance that a small segment may have been passed along whole for several generations. These small segments may be from an ancestor who lived so long ago that they are beyond genealogical records.

2.       Although a child receives an X-chromosome from his or her mother, it is unlikely that that X would represent 50 percent of their maternal grandfather and 50 percent of their maternal grandmother. It is more likely that some other random amount between 0 percent and 100 percent would be inherited as the chromosome recombines. Therefore, an ancestor is likely to be under-represented (i.e., less than 50 percent) or over-represented (i.e., more than 50 percent) in the X-chromosome. The natural distribution of “under and over” is always possible. Therefore, we could be looking at a segment that gives false information in regard to the generation in which we share the common ancestor. That is, the larger the segment, usually we deduce the closer the relationship and the smaller the segment the more distant the relationship.

Written for the GFO DNA Special Interest Group, 18 Jan 2015 and appeared in the GFO Bulletin, Volume 64, No. 3, March 2015.

GFO is the Genealogical Forum of Oregon in Portland Oregon.  See their website:  www.gfo.org

For more information about DNA, please con­sider getting Emily’s book, Genetic Genealogy: The Basics and Beyond which can be purchased online at AuthorHouse.com, Amazon.com, and Barnes and Noble in paperback or as an e-book. The book can be ordered at any bookstore.

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