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A guide on chromosomal variations

By Melanie Byrd, Molecular Biology Researcher.

mellythesciencegeek. Instagram video.

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The biology of gender, from DNA to the brain
By Karissa Sanbonmatsu. Ted Talk video. 2018
“How exactly does gender work? It’s not just about our chromosomes, says biologist Karissa Sanbonmatsu. In a visionary talk, she shares new discoveries from epigenetics, the emerging study of how DNA activity can permanently change based on social factors like trauma or diet. Learn how life experiences shape the way genes are expressed — and what that means for our understanding of gender.”

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Is there something unique about the transgender brain?

By Francine Russo, 2016.

"Some children insist, from the moment they can speak, that they are not the gender indicated by their biological sex. So where does this knowledge reside? And is it possible to discern a genetic or anatomical basis for transgender identity? Exploration of these questions is relatively new, but there is a bit of evidence for a genetic basis. Identical twins are somewhat more likely than fraternal twins to both be trans.
    Overall the weight of these studies and others points strongly toward a biological basis for gender dysphoria."

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On biological sex

Open Ocean Exploration @RebeccaRHelm  Dec 2019.  Twitter thread.

Rebecca is a biologist and an assistant professor at the University of North Carolina, Asheville USA.

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“Friendly neighborhood biologist here. I see a lot of people are talking about biological sexes and gender right now. Lots of folks make biological sex sex seem really simple. Well, since it’s so simple, let’s find the biological roots, shall we? Let’s talk about sex...

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If you know a bit about biology you will probably say that biological sex is caused by chromosomes, XX and you’re female, XY and you’re male. This is “chromosomal sex” but is it “biological sex”? Well...

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Turns out there is only ONE GENE on the Y chromosome that really matters to sex. It’s called the SRY gene. During human embryonic development the SRY protein turns on male-associated genes. Having an SRY gene makes you “genetically male”. But is this “biological sex”?

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Sometimes that SRY gene pops off the Y chromosome and over to an X chromosome. Surprise! So now you’ve got an X with an SRY and a Y without an SRY. What does this mean?

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A Y with no SRY means physically you’re female, chromosomally you’re male (XY) and genetically you’re female (no SRY). An X with an SRY means you’re physically male, chromsomally female (XX) and genetically male (SRY). But biological sex is simple! There must be another answer...

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Sex-related genes ultimately turn on hormones in specifics areas on the body, and reception of those hormones by cells throughout the body. Is this the root of “biological sex”??

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“Hormonal male” means you produce ‘normal’ levels of male-associated hormones. Except some percentage of females will have higher levels of ‘male’ hormones than some percentage of males. Ditto ditto ‘female’ hormones. And...

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...if you’re developing, your body may not produce enough hormones for your genetic sex. Leading you to be genetically male or female, chromosomally male or female, hormonally non-binary, and physically non-binary. Well, except cells have something to say about this...

Maybe cells are the answer to “biological sex”?? Right?? Cells have receptors that “hear” the signal from sex hormones. But sometimes those receptors don’t work. Like a mobile phone that’s on “do not disturb’. Call and call, they will not answer.

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What does this all mean?

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It means you may be genetically male or female, chromosomally male or female, hormonally male/female/non-binary, with cells that may or may not hear the male/female/non-binary call, and all this leading to a body that can be male/non-binary/female.

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Try out some combinations for yourself. Notice how confusing it gets? Can you point to what the absolute cause of biological sex is? Is it fair to judge people by it?

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Of course you could try appealing to the numbers. “Most people are either male or female” you say.

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Except that as a biologist professor I will tell you...

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The reason I don’t have my students look at their own chromosome in class is because people could learn that their chromosomal sex doesn’t match their physical sex, and learning that in the middle of a 10-point assignment is JUST NOT THE TIME.

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Biological sex is complicated. Before you discriminate against someone on the basis of “biological sex” & identity, ask yourself: have you seen YOUR chromosomes? Do you know the genes of the people you love? The hormones of the people you work with? The state of their cells?

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Since the answer will obviously be no, please be kind, respect people’s right to tell you who they are, and remember that you don’t have all the answers. Again: biology is complicated. Kindness and respect don’t have to be.”

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Gender: When the body and brain disagree

Researchers are trying to unravel the tangled roots of gender identity

By Amanda Leigh Mascarelli. Science News for Students. July 31, 2015

“By looking at someone’s body, or even mapping that person’s genes, ‘We can’t really answer the question of what identity is.’ That, he says, remains hidden within the inner workings of our brain.”

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The gender spectrum: A scientist explains why gender isn’t binary

By Cade Hildreth. April 22, 2021.

“Unfortunately for those who believe in a gender binary, it is not scientifically or medically correct. Gender can’t be binary, because it is a personal identity and is socially constructed.”

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Sexual hormones and the brain: An essential alliance for sexual identity and sexual orientation

By Alicia Garcia-Falgueras and Dick F Swabb. Endocrine Development 2010:17:22-35.

"The fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge. In this way, our gender identity (the conviction of belonging to the male or female gender) and sexual orientation are programmed or organized into our brain structures when we are still in the womb. However, since sexual differentiation of the genitals takes place in the first two months of pregnancy and sexual differentiation of the brain starts in the second half of pregnancy, these two processes can be influenced independently, which may result in extreme cases in trans-sexuality. This also means that in the event of ambiguous sex at birth, the degree of masculinization of the genitals may not reflect the degree of masculinization of the brain. There is no indication that social environment after birth has an effect on gender identity or sexual orientation."

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​​Stop using phony science to justify transphobia

Actual research shows that sex is anything but binary

By Simón(e) D Sun. Published in Scientific American, June 13, 2019.
“Contrary to popular belief, scientific research helps us better understand the unique and real transgender experience. Specifically, through three subjects: (1) genetics, (2) neurobiology and (3) endocrinology. So, hold onto your parts, whatever they may be. It’s time for ‘the talk’.” Simón(e) D Sun is a doctoral candidate in the Tsien Lab at New York University’s Neuroscience Institute.
 

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The weird history of the “sex chromosomes”
By Molly Webster. Ted Talk video. 2019
“The common thinking on biological sex goes like this: females have two X chromosomes in their cells, while males have one X and one Y. In this myth-busting talk, science writer and podcaster Molly Webster shows why the so-called “sex chromosomes” are more complicated than this simple definition — and
reveals why we should think about them differently.”
 

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