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Concepts: Inheritance

Roberta Estes

Inheritance.

What is it?

How does it work?

I’m not talking about possessions – but about the DNA that you receive from your parents, and their parents.

The reason that genetic genealogy works is because of inheritance. You inherit DNA from your parents in a known and predictable fashion.

Fortunately, we have more than one kind of DNA to use for genealogy.

Types of DNA

Females have 3 types of DNA and males have 4. These different types of DNA are inherited in various ways and serve different genealogical purposes.

Males Females
Y DNA Yes No
Mitochondrial DNA Yes Yes
Autosomal DNA Yes Yes
X Chromosome Yes, their mother’s only Yes, from both parents

Different Inheritance Paths

Different types of DNA are inherited from different ancestors, down different ancestral paths.

The inheritance path for Y DNA is father to son and is inherited by the brother, in this example, from his direct male ancestors shown by the blue arrow. The sister does not have a Y chromosome.

The inheritance path for the red mitochondrial DNA for both the brother and sister is from the direct matrilineal ancestors, only, shown by the red arrow.

Autosomal DNA is inherited from all ancestral lines on both the father’s and mother’s side of your tree, as illustrated by the broken green arrow.

The X chromosome has a slightly different inheritance path, depending on whether you are a male or female.

Let’s take a look at each type of inheritance, how it works, along with when and where it’s useful for genealogy.

Autosomal DNA

Autosomal DNA testing is the most common. It’s the DNA that you inherit from both of your parents through all ancestral lines back in time several generations. Autosomal DNA results in matches at the major testing companies such as FamilyTreeDNA, MyHeritage, Ancestry, and 23andMe where testers view trees or other hints, hoping to determine a common ancestor.

How does autosomal DNA work?

Every person has two each of 22 chromosomes, shown above, meaning one copy is contributed by your mother and one copy by your father. Paired together, they form the two-sided shape we are familiar with.

For each pair of chromosomes, you receive one from your father, shown with a blue arrow under chromosome 1, and one from your mother, shown in red. In you, these are randomly combined, so you can’t readily tell which piece comes from which parent. Therein lies the challenge for genealogy.

This inheritance pattern is the same for all chromosomes, except for the 23rd pair of chromosomes, at bottom right, which determined the sex of the child.

The 23rd chromosome pair is inherited differently for males and females. One copy is the Y chromosome, shown in blue, and one copy is the X, shown in red. If you receive a Y chromosome from your father, you’re a male. If you receive an X from your father, you’re a female.

Autosomal Inheritance

First, let’s talk about how chromosomes 1-22 are inherited, omitting chromosome 23, beginning with grandparents.

Every person inherits precisely half of each of their parents’ autosomal DNA. For example, you will receive one copy of your mother’s chromosome 1. Your mother’s chromosome 1 is a combination of her mother’s and father’s chromosome 1. Therefore, you’ll receive ABOUT 25% of each of your grandparents’ chromosome 1.

In reality, you will probably receive a different amount of your grandparent’s DNA, not exactly 25%, because your mother or father will probably contribute slightly more (or less) of the DNA of one of their parents than the other to their offspring.

Which pieces of DNA you inherit from your parents is random, and we don’t know how the human body selects which portions are and are not inherited, other than we know that large pieces are inherited together.

Therefore, the son and daughter won’t inherit the exact same segments of the grandparents’ DNA. They will likely share some of the same segments, but not all the same segments.

You’ll notice that each parent carries more of each color DNA than they pass on to their own children, so different children receive different pieces of their parents’ DNA, and varying percentages of their grandparents’ DNA.

I wrote about a 4 Generation Inheritance Study, here.

Perspective

Keep in mind that you will only inherit half of the DNA that each of your parents carries.

Looking at a chromosome browser, you match your parents on all of YOUR chromosomes.

For example, this is me compared to my father. I match my father on either his mother’s side, or his father’s side, on every single location on MY chromosomes. But I don’t match ALL of my father’s DNA, because I only received half of what he has.

From your parents’ perspective, you only have half of their DNA.

Let’s look at an illustration.

Here is an example of one of your father’s pairs of chromosomes 1-22. It doesn’t matter which chromosome, the concepts are the same.

He inherited the blue chromosome from his father and the pink chromosome from his mother.

Your father contributed half of his DNA to you, but that half is comprised of part of his father’s chromosome, and part of his mother’s chromosome, randomly selected in chunks referred to as segments.

Your father’s chromosomes are shown in the upper portion of the graphic, and your chromosome that you inherited from you father is shown below.

On your copy of your father’s chromosome, I’ve darkened the dark blue and dark pink segments that you inherited from him. You did not receive the light blue and light pink segments. Those segments of DNA are lost to your line, but one of your siblings might have inherited some of those pieces.

Now, I’ve added the DNA that you inherited from your Mom into the mixture. You can see that you inherited the dark green from your Mom’s father and the dark peach from your Mom’s mother.

These colored segments reflect the DNA that you inherited from your 4 grandparents on this chromosome.

I often see questions from people wondering how they match someone from their mother’s side and someone else from their father’s side – on the same segment.

Understanding that you have a copy of the same chromosome from your mother and one from your father clearly shows how this happens.

You carry a chromosome from each parent, so you will match different people on the same segment. One match is to the chromosome copy from Mom, and one match is to Dad’s DNA.

Here is the full 4 generation inheritance showing Match 1 matching a segment from your Dad’s father and Match 2 matching a segment from your Mom’s father.

Your Parents Will Have More Matches Than You Do

From your parents’ perspective, you will only match (roughly) half of the DNA with other people that they will match. On your Dad’s side, on segment 1, you won’t match anyone pink because you didn’t inherit your paternal grandmother’s copy of segment 1, nor did you inherit your maternal grandmother’s segment 1 either. However, your parents will each have matches on those segments of DNA that you didn’t inherit from them.

From your perspective, one or the other of your parents will match ALL of the people you match – just like we see in Match 1 and Match 2.

Matching you plus either of your parents, on the same segment, is exactly how we determine whether a match is valid, meaning identical by descent, or invalid, meaning identical by chance. I wrote about that in the article, Concepts: Identical by…Descent, State, Population and Chance.

Inheritance on chromosomes 1-22 works in this fashion. So does the X chromosome, fundamentally, but the X chromosome has a unique inheritance pattern.

X Chromosome

The X chromosome is inherited differently for males as compared to females. This is because the 23rd pair of chromosomes determines a child’s sex.

If the child is a female, the child inherits an X from both parents. Inheritance works the same way as chromosomes 1-22, conceptually, but the inheritance path on her father’s side is different.

If the child is a male, the father contributes a Y chromosome, but no X, so the only X chromosome a male has is his mother’s X chromosome.

Males inherit X chromosomes differently than females, so a valid X match can only descend from certain ancestors on your tree.

This is my fan chart showing the X chromosome inheritance path, generated by using Charting Companion. My father’s paternal side of his chart is entirely blank – because he only received his X chromosome from his mother.

You’ll notice that the X chromosome can only descend from any male though his mother – the effect being a sort of checkerboard inheritance pattern. Only the pink and blue people potentially contributed all or portions of X chromosomes to me.

This can actually be very useful for genealogy, because several potential ancestors are immediately eliminated. I cannot have any X chromosome segment from the white boxes with no color.

The X Chromsome in Action

Here’s an X example of how inheritance works.

The son inherits his entire X chromosome from his mother. She may give him all of her father’s or mother’s X, or parts of both. It’s not uncommon to find an entire X chromosome inherited. The son inherits no X from his father, because he inherits the Y chromosome instead.

The daughter inherits her father’s X chromosome, which is the identical X chromosome that her father inherited from his mother. The father doesn’t have any other X to contribute to his daughter, so like her father, she inherits no portion of an X chromosome from her paternal grandfather.

The daughter also received segments of her mother’s X that her mother inherited maternally and paternally. As with the son, the daughter can receive an entire X chromosome from either her maternal grandmother or maternal grandfather.

This next illustration ONLY pertains to chromosome 23, the X and Y chromosomes.

You can see in this combined graphic that the Y is only inherited by sons from one direct line, and the father’s X is only inherited by his daughter.

X chromosome results are included with autosomal results at both Family Tree DNA and 23andMe, but are not provided at MyHeritage. Ancestry, unfortunately, does not provide segment information of any kind, for the X or chromosomes 1-22. You can, however, transfer the DNA files to Family Tree DNA where you can view your X matches.

Note that X matches need to be larger than regular autosomal matches to be equally as useful due to lower SNP density. I use 10-15 cM as a minimum threshold for consideration, equivalent to about 7 cM for autosomal matches. In other words, roughly double the rule of thumb for segment size matching validity.

Autosomal Education

My blog is full of autosomal educational articles and is fully keyword searchable, but here are two introductory articles that include information from the four major vendors:

When to Purchase Autosomal DNA Tests

Literally, anytime you want to work on genealogy to connect with cousins, prove ancestors or break through brick walls.

Y DNA

Y DNA is only inherited by males from males. The Y chromosome is what makes a male, male. Men inherit the Y chromosome intact from their father, with no contribution from the mother or any female, which is why men’s Y DNA matches that of their father and is not diluted in each generation.

If there are no adoptions in the line, known or otherwise, the Y DNA will match men from the same Y DNA line with only small differences for many generations. Eventually, small changes known as mutations accrue. After many accumulated mutations taking several hundred years, men no longer match on special markers called Short Tandem Repeats (STR). STR markers generally match within the past 500-800 years, but further back in time, they accrue too many mutations to be considered a genealogical-era match.

Family Tree DNA sells this test in 67 and 111 marker panels, along with a product called the Big Y-700.

The Big Y-700 is the best-of-class of Y DNA tests and includes at least 700 STR markers along with SNPs which are also useful genealogically plus reach further back in time to create a more complete picture.

The Big Y-700 test scans the entire useful portion of the Y chromosome, about 15 million base pairs, as compared to 67 or 111 STR locations.

67 and 111 Marker Panel Customers Receive:

Y, mitochondrial and autosomal DNA customers all receive options for Advanced Matching.

Big Y-700 customers receive, in addition to the above:

Y DNA Education

I wrote several articles about understanding and using Y DNA:

When to Purchase Y DNA Tests

The Y DNA test is for males who wish to learn more about their paternal line and match against other men to determine or verify their genealogical lineage.

Women cannot test directly, but they can purchase the Y DNA test for men such as fathers, brothers, and uncles.

If you are purchasing for someone else, I recommend purchasing the Big Y-700 initially.

Why purchase the Big Y-700, when you can purchase a lower level test for less money? Because if you ever want to upgrade, and you likely will, you have to contact the tester and obtain their permission to upgrade their test. They may be ill, disinterested, or deceased, and you may not be able to upgrade their test at that time, so strike while the iron is hot.

The Big Y-700 provides testers, by far, the most Y DNA data to work (and fish) with.

Mitochondrial DNA

Mitochondrial DNA is passed from mothers to both sexes of their children, but only females pass it on.

In your tree, you and your siblings all inherit your mother’s mitochondrial DNA. She inherited it from her mother, and your grandmother from her mother, and so forth.

Mitochondrial DNA testers at FamilyTreeDNA receive:

Of course, Y, mitochondrial and autosomal DNA testers can join various projects.

Mitochondrial DNA Education

I created a Mitochondrial DNA page with a comprehensive list of educational articles and resources.

When to Purchase Mitochondrial DNA Tests

Mitochondrial DNA can be valuable in terms of matching as well as breaking down brick walls for women ancestors with no surnames. You can also use targeted testing to prove, or disprove, relationship theories.

Furthermore, your mitochondrial DNA haplogroup, like Y DNA haplogroups, provides information about where your ancestors came from by identifying the part of the world where they have the most matches.

You’ll want to purchase the mtFull sequence test provided by Family Tree DNA. Earlier tests, such as the mtPlus, can be upgraded. The full sequence test tests all 16,569 locations on the mitochondria and provides testers with the highest level matching as well as their most refined haplogroup.

The full sequence test is only sold by Family Tree DNA and provides matching along with various tools. You’ll also be contributing to science by building the mitochondrial haplotree of womankind through the Million Mito Project.

Combined Resources for Genealogists

You may need to reach out to family members to obtain Y and mitochondrial DNA for your various genealogical lines.

For example, the daughter in the tree below, a genealogist, can personally take an autosomal test along with a mitochondrial test for her matrilineal line, but she cannot test for Y DNA, nor can she obtain her paternal grandmother’s mitochondrial DNA directly by testing herself.

Hearts represent mitochondrial DNA, and stars, Y DNA.

However, our genealogist’s brother, father or grandfather can test for her father’s (blue star) Y DNA.

Her father or any of his siblings can test for her paternal grandmother’s (hot pink heart) mitochondrial DNA, which provides information not available from any other tester in this tree, except for the paternal grandmother herself.

Our genealogist’s paternal grandfather, and his siblings, can test for his mother’s (yellow heart) mitochondrial DNA.

Our genealogist’s maternal grandfather can test for his (green star) Y DNA and (red heart) mitochondrial DNA.

And of course, it goes without saying that every single generation upstream of the daughter, our genealogist, should all take autosomal DNA tests.

So, with several candidates, who can and should test for what?

Person Y DNA Mitochondrial Autosomal
Daughter No Y – can’t test Yes, her pink mother’s Yes – Test
Son Yes – blue Y Yes, his pink mother’s Yes – Test
Father Yes – blue Y Yes – his magenta mother’s Yes – Test
Paternal Grandfather Yes – blue Y – Best to Test Yes, his yellow mother’s – Test Yes – Test
Mother No Y – can’t test Yes, her pink mother’s Yes – Test
Maternal Grandmother No Y – can’t test Yes, her pink mother’s – Best to Test Yes – Test
Maternal Grandfather Yes – green Y – Test Yes, his red mother’s – Test Yes – Test

The best person/people to test for each of the various lines and types of DNA is shown bolded above…assuming that all people are living. Of course, if they aren’t, then test anyone else in the tree who carries that particular DNA – and don’t forget to consider aunts and uncles, or their children, as candidates.

If one person takes the Y and/or mitochondrial DNA test to represent a specific line, you don’t need another person to take the same test for that line. The only possible exception would be to confirm a specific Y DNA result matches a lineage as expected.

Looking at our three-generation example, you’ll be able to obtain a total of two Y DNA lines, three mitochondrial DNA lines, and 8 autosomal results, helping you to understand and piece together your family line.

You might ask, given that the parents and grandparents have all autosomally tested in this example, if our genealogist really needs to test her brother, and the answer is probably not – at least not today.

However, in cases like this, I do test the sibling, simply because I can learn and it may encourage their interest or preserve their DNA for their children who might someday be interested. We also don’t know what kind of advances the future holds.

If the parents aren’t both available, then you’ll want to test as many of your (and their) siblings as possible to attempt to recover as much of the parents’ DNA, (and matches) as possible.

Your family members’ DNA is just as valuable to your research as your own.

Increase Your Odds

Don’t let any of your inherited DNA go unused.

You can increase your odds of having autosomal matches by making sure you are in all 4 major vendor databases.

Both FamilyTreeDNA and MyHeritage accept transfers from 23andMe and Ancestry, who don’t accept transfers. Transferring and matching is free, and their unlock fees, $19 at FamilyTreeDNA, and $29 at MyHeritage, respectively, to unlock their advanced tools are both less expensive than retesting.

You’ll find easy-to-follow step-by-step transfer instructions to and from the vendors in the article DNA File Upload-Download and Transfer Instructions to and from DNA Testing Companies.

Order

You can order any of the tests mentioned above by clicking on these links:

Autosomal:

Transfers

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Disclosure

I receive a small contribution when you click on some of the links to vendors in my articles. This does NOT increase the price you pay but helps me to keep the lights on and this informational blog free for everyone. Please click on the links in the articles or to the vendors below if you are purchasing products or DNA testing.

Thank you so much.

DNA Purchases and Free Transfers

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