Let’s Talk About Sex

Sex is pretty simple: you’re either male or female, right?  Nope!  Turns out it’s not nearly that straightforward.  In fact, it’s pretty darned complicated.

AncestryDNA kit registration now asks for "Sex Assigned at Birth".That’s why a recent update at AncestryDNA is so welcome.  Like me, you may not have even noticed when it happened, but the DNA kit details now refer to “Assigned sex at birth” rather than “Sex”.

This is a big deal, because sex is more than skin deep.  What you learned in school is still true:  most of us either have two X chromosomes (denoted XX) and female anatomy or one X and one Y chromosome (XY) and male anatomy.  But it’s not the whole truth.

A child can have a single X (X0), three Xs (XXX), two Xs and a Y (XXY), or other combinations (XXXY, XYY, etc.).  What’s more, someone can have a Y chromosome and female anatomy, no Y and male anatomy, ambiguous anatomy, or even anatomy that does not align with their gender identity.

To understand why, we need to take a deep dive into what DNA actually does.


Bio 101

At its core, DNA is a set of instructions on how to build and operate a body.  For humans, you can think of it as a 23-volume set of loose-leaf binders (chromosomes 1–22 plus the X chromosome), with an optional section for some individuals (the Y chromosome).

 A stack of colorful loose-leaf binders.
Image by Gino Crescoli from Pixabay

Each page (gene) in a binder (chromosome) gives instructions for one part of the system.  The X chromosome has about 900 genes and is essential to life.  The body can’t operate without it.  Everyone has at least one X chromosome.

The Y chromosome, on the other hand, is much smaller and has only about 55 genes.  It’s not essential; half the human population does just dandy without one, after all.

There is one gene usually found on the Y chromosome that is key to male anatomy, though.  That gene is called SRY or sometimes TDS for testis-determining regionSRY is what’s called a regulatory gene; it tells other genes when to take action, a bit like a manager in an office directs other employees in their specific roles.  SRY is, in fact, upper-level management, because it controls other regulatory genes.


SRY and Anatomical Sex

Early in development, the SRY gene initiates a cascade of events that usually results in male anatomy.  If SRY does not function properly because of mutation, an XY fetus can have female appearance.  In other words, that child will be “chromosomally male” but anatomically female.

The biology gets even more interesting.  SRY isn’t always found on the Y chromosome.  It can sometimes end up on the X chromosome.  We don’t typically think of the X and Y chromosomes crossing over, but it’s normal at their very tips.

The so-called pseudoautosomal regions (PARs) are highlighted in yellow in the figure below.  Note where SRY is.  It’s just beyond the PAR, meaning that if a bit too much of the PAR swaps during sperm production, SRY can end up on an X chromosome.

The Y chromosome. Source: https://pubmed.ncbi.nlm.nih.gov/25814157/#&gid=article-figures&pid=figure-1-uid-0


A Y chromosome that has lost its SRY gene to crossing over will lead to female anatomy, and an X chromosome with SRY will induce male anatomy.  It’s also possible for SRY to end up on another chromosome entirely through an event called transposition.

Returning to the binder analogy, the “page” for SRY can sometimes get removed from the Y binder and put into another one.  The instructions it gives are the same, though.


So, SRY Makes a Male?

Whoa Nellie!  Not so fast.  Remember that SRY is the genetic equivalent of an executive manager.  If the staff don’t do their jobs, the project still doesn’t meet its goals.

One way that SRY delivers its message to the rest of the body is through hormones called androgens.  Testosterone is an androgen.  At high enough levels, androgens tell cells to develop male characteristics, both the obvious anatomical ones (genitalia) and secondary sexual traits like facial hair, muscle mass, and so on.

Androgens are made by a chemical assembly line, with each step regulated by a different gene.  If any of those genes don’t function properly, not enough of the “make-a-male” instruction gets out.

Even if the message gets out, it’s not always heard.  Body cells receive the message via special proteins called androgen receptors.  If the receptors don’t function properly, cells won’t receive the androgen signals and can’t respond.  People with androgen insensitivity can be anatomically male, female, or something in between, depending on degree of insensitivity.


There’s Still So Much to Learn

We’ve seen above that sex isn’t so simple; external anatomy might not align with one’s genetic makeup for any number of reasons.  What’s more, people with these conditions may not show symptoms until puberty, if at all.

And we’ve just scratched the surface.  There’s still plenty about anatomy, brain development, and gender identity that geneticists haven’t worked out yet.  It’s no wonder that some of us identify in ways that don’t fit the stereotypes associated with our genitalia.  It’s all part of the normal human rainbow.

That’s why AncestryDNA’s move toward inclusivity is so important.  While the presence of a Y chromosome may be important to genealogy, it’s not necessarily important to who we are.  And although a simple check-box can never reflect all of human diversity, I’m glad to see Ancestry acknowledge that we are not always the sex assigned based on anatomy at birth.

Painted pride colors
Photo by Steve Johnson on Unsplash

43 thoughts on “Let’s Talk About Sex”

  1. Call me a traditionalist, but I think Ancestry is engaged in obfuscation. What does “sex assigned at birth” mean? Is “sex assigned at birth” based on external anatomy, the presence or absence of the Y chromosome, or merely what is indicated on the birth certificate? In light of all the possible variations, then perhaps sex should be expressed in terms of percentages, similar to what is currently done with ethnicity. Then Ancestry could have a commercial that says “I thought I was this, but I found out that I was that.”

    1. “Sex assigned at birth” is usually based on external anatomy. For most of us, it’s the sex we identify as, but for others, it’s not, for any number of reasons. You’re right that sex isn’t necessarily all-or-none. Some people are male, some are female, some are both, and some are neither. It’s nice to see Ancestry acknowledge that.

  2. Wow! This information really sheds light and facts on what we see is not always what it seems. This article sheds light on the adage ” Don’t judge a book by its cover”.

  3. You are confusing biology. If a person has anything other than xx or XY they are intersex, which is NOT trans. Even with all your historical experience, you chose to swallow the gender identity narrative, even though it is based on ideology, not science.

    Ancestry…what a joke.

      1. The “Gender Identity” narrative is itself ideology and not science. There is a big difference between these people who have a known psychological disorder which is transgenderism (aka gender dysphoria), and those who have rare x and y combinations. Gender dysphoria can be cured using anti-psychotics, which is what should happen considering most that transition commit suicide afterwards or de-transition. But hey what do I know I am only someone who suffered gender dysphoria and was cured with Anti-psychotics myself when I was younger.

        1. I can tell that the trans issue is important to you because you brought it up in response to a post about a different subject: the SRY gene and the X & Y chromosomes. Being trans is not a psychological disorder and does not need to be “cured”. I’m sorry that you were given anti-psychotics rather than being affirmed for who you are.

        2. Actually you brought up the Trans issue by saying Gender identity, and it is a psychological disorder and has been, it’s in the Diagnostical and Statistical Manual of Mental Disorders (DSM-5). These people do no need “Affirmation” they need psychological help. Unfortunately people prefer to coddle and affirm mentally disturbed people now days which does more harm than good. This is why they commit so many suicides after Transitioning. Would you affirm a psychopath or someone who is suicidal?

        3. The American Psychiatric Association, which publishes the DSM-5, says “Diverse gender expressions, much like diverse gender identities, are not indications of a mental disorder.”

          I will quote their treatment section in full. The italics are mine:
          Support for people with gender dysphoria may include open-ended exploration of their feelings and experiences of gender identity and expression, without the therapist having any pre-defined gender identity or expression outcome defined as preferable to another.2 Psychological attempts to force a transgender person to be cisgender (sometimes referred to as gender identity conversion efforts or so-called “gender identity conversion therapy”) are considered unethical.2,3

          Support may also include affirmation in various domains. Social affirmation may include an individual adopting pronouns, names, and various aspects of gender expression that match their gender identity.4,5 Legal affirmation may involve changing name and gender markers on various forms of government identification.6 Medical affirmation may include pubertal suppression for adolescents with gender dysphoria and gender-affirming hormones like estrogen and testosterone for older adolescents and adults.7, 8 Medical affirmation is not recommended for prepubertal children.7, 8 Some adults (and less often adolescents) may undergo various aspects of surgical affirmation.7, 8

          Family and societal rejection of gender identity are some of the strongest predictors of mental health difficulties among people who are transgender.9 Family and couples’ therapy can be important for creating a supportive environment that will allow a person’s mental health to thrive. Parents of children and adolescents who are transgender may benefit from support groups. Peer support groups for transgender people themselves are often helpful for validating and sharing experiences.”

          Please read it: https://www.psychiatry.org/patients-families/gender-dysphoria/what-is-gender-dysphoria

      2. “Being trans is not a psychological disorder and does not need to be “cured”

        If someone chooses to be “cured”, why are surgical and hormonal treatments allowed to convert a physical body to mimic the other sex but treatments or psychological therarpy to become more comfortable in the present physical body i.e. Gay Cure are banned by law ?

        1. You seem to be conflating homosexuality with being trans. They are not the same thing, and neither one is a disorder that needs to have a “cure” forced upon the individual. So-called “conversion therapy” can have adverse outcomes, including depression, drug use, and suicide. That is why it is banned by law.

    1. 45, X is not intersex. 47, XXY is not intersex. Just two examples of Blue Jay not understanding biology.

      Thank you for this post, Leah!

    2. You said ‘swallow’! LOL! 😀
      Just tryin’ to add levity where I feel it’s helpful… At the end of the day, who cares what somebody else identifies as? If it makes them happy or helps them to get a little closer to happiness, I’m happy for them. Besides, happy people are more fun to be with & share the planet with. 🙂

  4. Brilliant explanation, much needed technical (reality) info. Thank You so much Leah.
    We all should be reminded that we don’t always know the truth, but the more of it we do know, the more “The Truth Will Set You Free”.

  5. The question is, what % of the population has these variations? If it is one in a multiple of thousands, isn’t Ancestry’s move overkill? Genealogy is about what is, not what we wish it was.

    1. That’s a great question! Individually, each of these conditions is rare, but as a whole, they add up. I’ve seen estimates that up to 1.7% of the population is intersex, 0.6% is trans, and perhaps 5% LGBT. The nice thing about this change at Ancestry is that it acknowledges these relatives without inconveniencing anyone else.

      1. “I’ve seen estimates that up to 1.7% of the population is intersex, 0.6% is trans, and perhaps 5% LGBT”

        “Up to” is a method used to inflate the frequency of occurance. Since LGBT+ is self-reported but tallied by survey questions, the counting method needs to be considered. One pop article categorized responses e.g G and B and used the sum, not mutual exclusion, to inflate LGBT numbers.

        Past and present methods of counting LGBT include a single sexual experience or feelings of attraction towards a person of the same sex even when those feelings did not lead to a sexual encounter

        1. Estimates are, by definition, imprecise. Given the stigma still associated with LGBTQ, one could argue that the numbers are underestimates; many people may claim to be heterosexual, even if they aren’t, to avoid social disapproval. Scientific studies of physiological arousal suggest that there is a continuum of orientations in both men and women. That is, some of us are heterosexual, some of us are homosexual, and some of are both to varying degrees.

    2. Ancestry has 3 million paying subscribers. The conservative estimate is that the prevalence of intersex (in its strictest sense) is about 0.018%. That might suggest 540 Ancestry subscribers. I think it makes smart business sense to have a product that works for all customers not just most.

      Overkill? not remotely.

    3. I used to know a ‘man’ in his ’60’s who was very sweet but very odd. He told me once (& I fully believed him) that he was born with both sets of reproductive organs – and, he was one of the few like that, that was not castrated at birth. However, his penis was too small to use & he was so socially awkward, it had not been an issue. He dies a virgin.
      This is a true story. He was a sweet man. It was very sad.

  6. Thank you for writing this article. It is very helpful to understanding such a complex science. The “binder” analogy is spot on!

  7. Thanks for the lesson, Leah. I’s an interesting and timely topic. Though, I’m not clear how this change at Ancestry is impactful or inclusive. Assigned sex at birth is the doctor 50 years ago noting whether I was born with a penis or a vagina. How is asking that question a step toward being inclusive? Also, what is the impact of choosing one or the other? Is it that I will be a Blue or Pink silhouette to my matches if I don’t have a picture? Doing away with the Blue/Pink colors and letting us choose our own palette, that would be a positive step toward inclusivity.

    1. Assigned sex is relevant to genealogy, because that’s what will be on the birth records, even if it’s wrong. I like your idea of letting us choose our own palette for the silhouettes!

  8. Yep, they use that field to determine what color silhouette your matches see in the absence of a profile photo. I would actually view this as not a positive move by Ancestry. If my gender identity was something different than what my doctor observed 50 years ago, I would rather my color silhouette on Ancestry reflect my identity, not my doctor’s observation. And if this is the only use for this piece of information, there should be a choice to choose neither.

  9. “But God created all species as males and females, just like us”, he said. The Blue-headed Wrasse in his aquarium demurred. Fortunately the banana slug in the garden wasn’t listening.

    I have wondered how Ancestry would eventually work this into their database. I have both a Trans cousin and a you-either-have-a-penis-or-not cousin. Good to see your article for perspective.

      1. [insert Dr. Tatiana’s insightful comment here.] (For several years, my wife taught a non-major’s course called “The Biology of Sex”; her students could never come to grip with sex in Slime Molds.)

        1. Ooo, another Dr Tatiana fan! Olivia Judson was the keynote speaker at the Evolution conference in 2008, and she was fabulous. She said that she was working on another book at the time. It’s a shame that it never came to be.

  10. Where is this info located in ancestry? My DNA was done a while ago and I cannot seem to find it in my profile.TY

  11. And that really matters, because if you have YDNA you can do a Y test.
    Oh wait, they don’t do that any more.
    So what they might be asking is, are you XX or XY, because XX have a little more DNA.
    Otherwise, does it really matter in the DNA part?
    Surely it’s just in how we present ourselves to others.
    And some people already choose not to select one of the binary options anyway.
    Do any of the suffer by it? Not so I have noticed.

  12. “Pop-science” didn’t come up with this “new” concept of a gender spectrum. I have been taking the University of Alberta’s Indigenous Studies course and it has been a fact that many Indigenous Peoples have always understood.

  13. You educated this Grandmother today. Thank you for that, I always knew there was more than Male & Female but had no idea we really should be doing DNA at birth before checking one of many boxes.

  14. Sex isn’t “assigned” at birth. It’s observed. Intersex doesn’t disprove that there are only 2 sexes, they actually reinforce that. Intersex are all mostly infertile partial variations on the two functional sexes. Intersex are an insignificant fraction of people. And the majority of intersex generally developed towards one sex or the other and that’s how they live their lives. We don’t need to upend all of humanity because a handful of people have a genetic mutation.

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