Tag Archives: X chromosome

Down the DNA Rabbit Hole – X chromosome

I recently attended an all day genealogy seminar. Overall, the day was a success. After lunch, I intended to listen to a lecture on the importance of encouraging family members to preserve their history for future generations. Unfortunately, the speaker didn’t show up. At that point my choices were limited, so I chose to attend a lecture on beginning DNA research. Ordinarily, I wouldn’t have bothered, but I am curious to see how other speakers handle the topic. The speaker was very entertaining, and he covered the basics. However, I was extremely dismayed to hear him treat mtDNA and the X-chromosome as BASICALLY THE SAME THING. He couldn’t have been more wrong! And he did an extreme disservice to the audience, who were mostly inexperienced newcomers who didn’t know the difference between y-DNA, mt-DNA, and autosomal DNA, let alone understand the difference between the X-chromosome and mt-DNA.

When genetic genealogists talk about autosomal testing, they are referring to the twenty-two pairs of autosomes that make up the human roadmap. Currently, the autosomal DNA test is the most widely administered DNA test for genetic genealogy. In addition to the twenty-two autosomes, all humans have a pair of sex chromosomes, also known as chromosome pair twenty-three. A female receives two X-chromosomes, one from each of her parents. A male receives one X-chromosome from his mother, and one Y-chromosome from his father. The Y-chromosome makes a baby a male, and is only inherited from the male parent. Sadly, Henry VIII didn’t know this in the 16th century and blamed his wives for the lack of a male heir. The Y-chromosome test was the first DNA test made available to genealogists well over a decade ago. Only males can take this test. When a person takes an autosomal DNA test, their X-chromosome(s) is/are included in the test.

Gladys (Foster) Yegerlehner, 1929

Because of the unique way that the X-chromosome is passed down, hopscotching it’s way over male descendants, tracing X-chromosome matches can rewarding. [On a side note – because the X-chromosome sometimes skips generations, it often experiences less recombination. In practice, this means that a cousin match can actually be farther back than predicted.] A perfect example is my son’s X-chromosome. He only inherited one…from me. It turns out that he did not receive a recombined X-chromosome. Typically, part of the X-chromosome of my father and part of the X-chromosome of my mother would have been broken apart into segments and then pieced back together to create one whole X-chromosome for my son. What my son received was the entire X-chromosome from my father, without any recombination. And where did my father receive his X-chromosome? From his mother (and in case if you have been following my blog for the last five years, you are very familiar with her!), Gladys (Foster) Yegerlehner. So my son is the recipient of an entire chromosome that he received directly, un-recombined, from a single great grandmother. And doing the math, this specific X-chromosome has been around for three generations. If my son has a daughter, it will survive for another generation as well.

X one-to-one comparison between my father and my son (Image from Gedmatch)

There are some great charts available to help keep track of one’s X-chromosome inheritance. Below is a female X-chromosome chart with the data filled in from my family tree. I only filled in the ancestors who would have potentially provided me with a segment of their X-chromosome.

Female X-chromosome chart (created by Sue Griffith) with Deborah’s potential X-chromosome contributing ancestors

Resources for X-chromosome Charts:

Blaine Bettinger has male and female charts available on his website. Don’t forget to read his in-depth blog posts about the subject as well.

Debbie Parker Wayne has made several charts available on the publication page of her website.

Sue Griffith has versions of X-chromosome charts on her website:

©2017 Deborah Sweeney
Post originally found:  https://genealogylady.net/2017/04/25/down-the-dna-rabbit-hole-x-chromosome/