Is X-DNA helpful in genetic genealogy? - A Segment of DNA

we learn from pirates that x marks the spot but when it comes to DNA does X really help us any [Music] howdy I'm Andy Lee with family history fanatics and this is a segment of DNA today I wanted to talk about the X chromosome and how we could use the X chromosome to help us in our research and what limitations it actually has so there are five principles that I want you to remember about X DNA and I'm gonna go over them today for principle number one is our inheritance patterns are different how males and females get their X DNA is going to be different so let's take a look at how males and females inherit their X DNA so for males we have an X chromosome and a Y chromosome do we get the Y chromosome for our father which means we get the X chromosome from our mother so if you start right here you can see that all of the X DNA is coming from the mother's side and every time there is a male in the lineage so with your grandfather your great-grandfather that also is going to eliminate some of those people that you could have received DNA from because you don't so X DNA from the male side a hundred percent of it comes from the mother which means that 50 percent of it comes from each grandparent on average and then as you go the next generation back one side has 50% coming from the grandmother and the other side has 25% coming from each grandparent and this pattern continues on throughout the different generations so with females they have two x chromosomes they received one x chromosome from their father in one x chromosome from their mother and so this starts out very similar to autosomal DNA where you would expect 50% from the father 50% from the mother but as you go back in each generation beyond that just like with males you start to eliminate any chance of receiving DNA from the male line so for instance the father of a daughter only got his ex DNA from his mother so that paternal line no longer has any ex DNA being contributed to that granddaughter likewise on the mother's side this pattern is the same as what we saw on the male side so each one males and females receives slightly different inheritance of ex DNA and that's important when we're looking at any matches that involve XDM so principle number two because we're only looking at one chromosome we don't actually follow this 50% inheritance exactly now with females they do inherit 50% of their ex DNA from their father and 50% from their mother because they receive a full chromosome from their father and a full chromosome from their mother they also received that same full chromosome from their paternal grandmother now beyond that the amount of ex DNA that you received from any great grandparent or great great grandparent is really dependent on recombination and that is a random process that may give you large chunks or small chunks it may give you 3 or 4 segments or it may just give you one segment so you can't use a table of percentages to estimate back how many generations you are because your lines follow different ways and you're only dealing with one chromosome so there's not enough to keep that 50% overall now over a whole population on average yeah it's going to follow that 50% ratio but on an individual basis we're just dealing with one chromosome here so we can't use that assumption so principle number three is if you have an X DNA match without any autosomal DNA match that match is probably distant enough that you're not going to be able to determine how you're related so when you're looking at X DNA make sure you're focusing on those that you also share some autosomal DNA with now the fourth principle is X DNA is an excellent elimination tool it tells you who you don't need to go and look at as you saw from the inheritance patterns every male in the line takes away the X DNA from before them for males and that can eliminate a lot of your tree so if you do have a match on autosomal DNA that you also have an X DNA match if you are male or if you are female the number of ancestors you actually have to look at is different let's use a couple of examples so if we are four generations back so your parents your grandparents your great-grandparents your great-great grandparents this would be third cousins you have sixteen great-great grandparents and so with an autosomal match you might have to look through 16 different lines to try to figure out which one is who you are related through however if you're male because of all the people you can eliminate that you didn't inherit any X DNA from you only have to look at five lines and if you're female you still get a benefit because you only have to look at eight lines so you only have to look at a third to half of all the possibilities with an X DNA match and that's at four generations it gets better the further back you go now looking at six generations this is about the extent of where autosomal DNA genealogical DNA testing is going to provide a good solid match to you have 64 and this would be your fourth great-grandparents so your fifth cousins which is pretty distant you have 64 fourth great-grandparents that normally on autosomal DNA you'd have to figure out which one is where you're related to but with that X DNA match if you're male you only have 13 less than a order of the total fourth great-grandparents that you have to look at because you've eliminated all the others and if you're female you still get a good benefit only twenty one less than a third of all of the potential fourth great-grandparents that you have to look at to find how that relationship is so X DNA is an excellent elimination tool now the fifth principle is something I've actually talked about through this whole thing and that is you have to understand the difference between males and females when it comes to X DNA matching and who you could possibly match up with because that inheritance pattern is different if you have a match in your female and that X DNA matches with a male then you're using two different inheritance patterns when you're looking at your two trees and you got to remember to keep that separate so that you can eliminate the most possible people and also be able to find matches that you have autosomal matches with as well using your X DNA so if you have any questions about how you can use X DNA in your genetic research put it in the comments below and we'll try to help you out if you like this video be sure to give it a thumbs up so they can reach more viewers be sure to check out our website WWE history fanatics calm so that you can find out about upcoming conferences that we're going to be a part of [Music] you [Music]

Channel: Family History Fanatics

Views: 17,649

Rating: 4.9269104 out of 5

Keywords: genealogy, family history, family tree, ancestry, family search, genetic genealogy, x dna, X-DNA, dna test, dna test results, familytree dna test results, what is x dna, What XDNA, what is x dan, dna tutorial, education, explanation

Id: Cl2pJrLwbVU

Length: 8min 6sec (486 seconds)

Published: Tue Mar 20 2018