Consider Erin Mendel, a member of the family whose data is visible both to customers and holders of free demo accounts. Using the Compare Genes feature (reproduced below), you can see that among the genes associated with pigmentation Erin is closest to her brothers and mother, and less like her father Greg.

The Cards You’re Dealt

Assign each of your grandparents a suit – spades, hearts and so on – in a deck of cards. In the game of inheritance, their chromosomes (or chunks of genes) are shuffled (or recombined) and then dealt to their children so that each grandparent contributes one chromosome out of each pair. Your dad then ends up with 23 chromosomes of one suit from his father, and 23 of another from his mother. Your mom has a similar set of paired chromosomes from her two parents. So when your parents’ chromosomes

are shuffled, mixed together and dealt in turn to you and your siblings, you end up with a mix of chromosomes bearing all four of your grandparents’ suits. The illustration on the right shows the proportion of her genes that Erin inherited from each grandparent.

Since each child’s genetic information is produced by shuffling and dealing a new hand from the same genetic deck, there are going to be segments on their chromosomes where siblings are completely identical (having gotten the same suits from mom and dad). If a pair of siblings got the same chromosomal segment from one parent, but not from the other, they will be what geneticists call “half-identical.” In general, parents are half-identical to their children everywhere, because they passed their offspring one out of each pair of chromosomes. The exception is when two parents are related to each other.

Family Comparisons
Using the Family Inheritance option, Erin can see which segments she shares in common with various members of her family.

On the Genome-Wide Comparison chart, bars representing the 22 chromosomes and both X and Y chromosomes can be dark blue (representing a full match), light blue (“half-identity”), white (no match) and gray (not enough information). Below is a comparison of Erin and her father, showing only the first six chromosomes. Erin is only half-identical to her dad throughout her genome because one of her chromosomes out of each pair came from her mom Lilly.

So what does this all mean? Let’s consider the following example. When Erin compares herself to other people at the immune system compatibility trait, she sees red triangles above a region of chromosome 6 known as the MHC, or major histocompatibility complex. The human MHC is known as the HLA (human lymphocyte antigen) system. These genes determine how the immune system recognizes and distinguishes bacteria and other foreign invaders from the body’s own tissues. Aside from tests to verify that the blood types of donor and recipient match, the HLA system is what gets checked to minimize the chances that a transplant recipient’s immune system will reject the organ or tissue donated.

Because they are unrelated, Erin’s parents Greg and Lilly have no identical segments in the HLA system so they probably wouldn’t be a good match for each other. One’s histocompatibility, as this gene harmony matching process is known, is inherited.

On the other hand, Erin might decide to make sure her brother Ian gets great birthday and Christmas presents from now on. When Erin does the one-on-one comparison with Ian using the Family Inheritance option, the results on the right suggest that he might be the best match for her if she ever needs a new kidney or some bone marrow. With “completely identical” HLA systems, the chances are good that they could donate marrow or a kidney to each other without immune rejection.

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Click here to learn more about what 23andMe’s Personal Genome Service™ can and can’t do with regard to unknown parents:

Ancestry

23andMe’s Personal Genome Service™ offers a number of different tools for probing your ancestry. The broadest view comes from the Global Similarity feature, which identifies the native populations around the world you most resemble genetically. It is likely the majority of your ancestors came from the one or two regional populations that are most similar to you.

The Maternal Ancestry feature offers a different vantage point, using one specific part of the genome to trace a single branch of your family tree back in time and space. The results apply to only one branch – your mother’s all-female lineage – but they trace it all the way back to the origin of the human species about 200,000 years ago. As a result, the Maternal Ancestry feature gives you a very good idea of where your mother’s mother’s mother’s … family came from.

The Paternal Ancestry feature provides similar information, except that it provides information about a person’s all-male ancestral line. Because it analyzes DNA on the Y-chromosome, however, it is only available for men.

Finally, 23andMe recently introduced the Ancestry Painting feature, a new component of our service that could be of great interest to people who are uncertain about their heritage. Ancestry Painting examines each stretch of a person’s DNA and determines which of three continents it most likely came from – Africa, Asia or Europe. Because each person gets a complete set of chromosomes from each parent, the Ancestry Painting feature can tell an adopted person what continent each of his or her parents’ ancestors came from. The daughter of an African-American mother and an Asian-American father, for example, could easily see that signature in her Ancestry Painting.

Family Relationships

The data produced by 23andMe’s Personal Genome Service™ is not a tool to locate unknown parents. But it can be useful for determining the relationships between people. If you suspect another person might be related to you, you could test that theory (as long as that person also signs up for 23andMe and agrees to share profiles). For example, if you and a half-sibling compared yourselves to one another you would find that you share substantial stretches of half-identical DNA.

Health and Physical Traits

Most people make assumptions about some of the genetic variants they have inherited by looking at their parents and grandparents. A family history of heart disease, cancer or diabetes, for example, may indicate that a person has inherited some genetic predisposition for that particular ailment.

Naturally, people who do not know their parents have no idea about any disease-related genetic variants they might have inherited. While 23andMe does reveal some genetic information about genetic variations that have been associated with diseases and conditions, it does not offer a full enough view to establish a family history.

Because genetics is only one among many factors that can influence a person’s health and physical traits (and often only a minor factor!) there is very limited definitive information 23andMe can provide about unknown parents’ physical appearance or medical history. But even at this early stage of research, 23andMe can give you a glimpse at your parents’ DNA simply by showing you your own, along with the results of recent scientific studies that give it context. And over time, we hope to learn much more about how genetic information translates into physical traits and health outcomes.

Photo by Nancy Catherine Walker/iStockphoto

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