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.
INHERITANCE
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.
FEMALE INHERITANCE WITHOUT PERCENTAGES
1
|
15
|
43
|
62
|
106
|
125
|
183
|
219
|
246
|
2
|
21
|
45
|
63
|
107
|
126
|
186
|
221
|
247
|
3
|
22
|
46
|
85
|
109
|
127
|
187
|
222
|
250
|
5
|
23
|
47
|
86
|
110
|
170
|
189
|
223
|
251
|
6
|
26
|
53
|
87
|
111
|
171
|
190
|
234
|
253
|
7
|
27
|
54
|
90
|
117
|
173
|
191
|
235
|
254
|
10
|
29
|
55
|
91
|
118
|
174
|
213
|
237
|
255
|
11
|
30
|
58
|
93
|
119
|
175
|
214
|
238
|
|
13
|
31
|
59
|
94
|
122
|
181
|
215
|
239
|
|
14
|
42
|
61
|
95
|
123
|
182
|
218
|
245
|
Figure 1 from Genetic Genealogy: The Basics
and Beyond, p. 43
MALE INHERITANCE WITH PERCENTAGES
1
|
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.
FINDING COMMON ANCESTORS
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.
CREATING AN X-CHROMOSOME AHNENTAFEL
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
Figure 5: ANCESTORS OF EMILY DOOLIN
for X Chromosome Matches
GENERATION NO. 1
1. Emily Doolin
GENERATION NO. 2
2. Donald Doolin
3. Beverly Williams
GENERATION NO. 3
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.
GENERATION
NO. 4
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.
GENERATION
NO. 5
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.
SUCCESS VS. NO SUCCESS
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.
SUMMARY
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.
ENDNOTES
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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