SRY gene = male
No SRY gene = female

This is accurate at a rate of 99.99% - 99.999%. This is even more accurate than testing purely for chromosomes. We can test for this gene in advanced yet now common karyotyping techniques that we can do very quickly.

Exceptions to this occur most often when male or female genetic networks downstream of SRY are activated or repressed due to various mutations, leading to male or female development. See this wonderful thread by Emma on the history of chromosome and gene testing. Scroll to the top to see the beginning. Though this specific post I quoted below is incredible.

We’ve advanced way beyond merely looking at just the chromosomes or Barr bodies.

https://twitter.com/fondofbeetles/status/1821905798336770391

From the Court of Arbitration for Sport back in 2018, still relevant to today, regarding the Caster Semenya case:

"It would be irrational and arbitrary to treat 5-ARD athletes in the same way as 46 XX female athletes simply because they have the same legal sex and/or gender identity. Legal sex and gender identity each have no bearing on athletic performance. Nor do the appearance of the external genitals. Levels of serum testosterone, on the other hand, do have such a bearing.

In particular, 5-ARD individuals have all the ergogenic physiological advantages of high testosterone levels that adult males have, irrespective of their natal or legal sex, their gender identity or the appearance of their genitals.

It follows that allowing individuals to participate in the female category simply on the basis of their legal sex or gender identity would not deliver the protection from unfair competition that the broad class of female athletes is entitled to."
tas-cas.org/fileadmin/user… "Just as it is unfair for a female athlete with ovaries to have to compete against a male athlete with testes that produce 15 times more performance-enhancing endogenous testosterone than she does, equally it is not fair for that female athlete to have to compete with a 5-ARD athlete with those same physical traits."

Those are karyotypes, a person's chromosome profile, not genotypes, which is the full genetic (gene) profile.

This is basic stuff that a geneticist like you should already understand at undergrad or high school level way before getting a PhD.

Each of those karyotypes results in a male or female, not someone who is "between" sexes. Why? Because genetic sex determination in mammals is binary, even in cases of unusual chromosome configurations.

I'll show you how below. Take XO. It is a chromosomal disorder in females. Even though they are missing the second X chromosome typically seen in females, they still develop a reproductive system organized around egg production because the female genetic pathway is upregulated.

No SRY gene means that WNT4, RSPO1, and FOXL2 can say "make ovaries" and the fetus differentiates down the female path.

The only way to treat their infertility, hormonal issues, and other medical problems is first knowing that they are female.

What are the effects of blocking puberty in females?

Pubertal development in females requires the reception of sex hormones through the hypothalamic-pituitary-gonadal axis. Block this axis, as puberty blockers do, and you'll end up with a host of physical and cognitive issues.

Researchers have tested the effects of blocking this axis in female mice. For example, when puberty suppressors are given to female mice, there is reduced bone mass acquisition and bone strength; increased risk of obesity; decreased uterine and ovarian weights; completely absent follicle maturation (no mature eggs produced); and a lack of a reproductive cycle. In females, reproductive cycles create cyclical hormone levels of estrogen and progesterone that rise and fall, essential for maintaining healthy anatomy and physiology.

On the psychological and behavioral level, there is inhibition of feeding (hyponeophagia) matched with hyperactivity in the dentate gyrus of the hippocampus, signifying high anxiety; despair-like behavior; and negative mood regulation.

In other animals like sheep, it's been shown that blocking puberty also permanently impairs long-term spatial reference memory even after the drugs are stopped, reflecting a time-limited period of hippocampal plasticity where a specific window around puberty is required for its maturation. This is particularly concerning knowing that the hippocampus is essential for learning, memory, and spatial navigation.

These findings in mice and sheep match with what we see in trans-identifying females whose puberty is blocked by gonadotropin-releasing hormone (GnRH) antagonists and agonists, which reduce sex hormone levels to castration levels within 30 days and halt the reproductive cycle. In human females, GnRH analogue usage around puberty increases emotional reactivity, including emotional and behavioral responses to fearful situations; decreases long-term decision making; and it also decreases the resting heart rate. It also is associated with a higher risk of osteoporosis and cardiovascular disease.

GnRH analogues have their place in medicine, but they are not designed to be used long term at consistent doses and certainly not to block puberty, where the important physical and neurological maturation is essential for long term health.

[1] Dela Cruz, C., Kinnear, H., Hashim, P., et al. (2023). A mouse model mimicking gender-affirming treatment with pubertal suppression followed by testosterone in transmasculine youth. Human Reproduction, 38(2).

[2] Anacker, C., Sydnor, E., Chen, B., et al. (2021). Behavioral and neurobiological effects of GnRH agonist treatment in mice—potential implications for puberty suppression in transgender individuals. Neuropsychopharmacology, 46.

[3] de Tassigny, X., Fagg, L., Dixon, J., Colledge, W. (2007). Hypogonadotropic hypogonadism in mice lacking a functional Kiss1 gene. Biological Sciences, 104(25).

[4] Xu, L., Li, H., Liu, S., et al. (2022). Constitutional delay of growth and puberty in female mice is induced by circadian rhythm disruption in utero. Ecotoxicology and Environmental Safety, 241.

[5] Hough, D., Bellingham, M., Haraldsen, I., et al. (2017). Spatial memory is impaired by peripubertal GnRH agonist treatment and testosterone replacement in sheep. Psychoneuroendocrinology, 75.

[6] Novara, G., et al. (2009). Impact of Surgical and Medical Castration on Serum Testosterone Level in Prostate Cancer Patients. Urol Int, 82(3). I wrote about males here:
x.com/zaelefty/statu…

I present my new book on debunking the sex spectrum!

Order now on Amazon!

I tackle 10 common sex spectrum arguments and teach the reader how to respond with detailed knowledge from evolutionary and developmental biology literature.
amazon.com/Binary-Debunki…
This book was a culmination of two and a half years of work, from the initial concept phase to publishing.

It was created due to the responses I received from you all, my followers, who enjoyed my initial threads debunking sex spectrum arguments here on Twitter, from Nature's "Sex Redefined" and SciAm's "Stop Using Phony Science" to ScienceVet's infamous thread or Anne Fausto-Sterling's paper on the false 1.7% "intersex" statistic.

The book features expanded versions of these threads and more!

From a peer-reviewed paper on male lactation: “We should therefore rethink what successful breastfeeding means. The main goal of lactation induction in transgender women may not necessarily be milk production, but rather the nonnutritional benefits that come from breastfeeding.” Many of the peer-reviewed papers praising breastfeeding in trans women are examples of how gender ideology has captured the research process.
academic.oup.com/jcem/article/1…

Let’s clarify genotype and phenotype and how these terms relate to sex 🧵 1. What is genotype?

Genotype is the complete set of an organism’s genes.

People often confuse genotype for the collection of chromosomes (karyotype) but genotype is about the genes within the chromosomes.

This is sick and anti-science. All these development disorders result in males or females.

I will explain how below.

https://twitter.com/plasticmartyr/status/1648387076256337922

Let’s start with Swyer Syndrome.

It occurs when male sex determining genes like SRY are absent in an XY fetus, which then allows the fetus to go down the female path.

This results in anatomy organized around eggs (female).

If you are going to read one scientific paper on biological sex, read this one.

It’s the quintessential manifesto for articulating why sex is binary, written in the peer-reviewed journal BioEssays.
onlinelibrary.wiley.com/doi/10.1002/bi… This paper covers many of the principles I’ve written about and many of the scientific papers I’ve used on the biology of sex.

If you do not want to wait for us to raise more funds, DM me if you’re interested in buying a batch ASAP of 50, 100, or 250 professionally printed pamphlets on the myths of gender affirming care.

We want to spread these far and wide! View and download the pamphlet and sources here.
theparadoxinstitute.com/print/pamphlet…

We’ve received print requests for a total of 300+ professional pamphlets summarizing the harms of gender affirming care in children.

If you’re interested in receiving a batch for yourself or your group, contact us @ theparadoxinstitute@gmail.com Inside the pamphlet provides a detailed overview of the data.

Rare genetic disorders like this one (46:XY CBX2 negative female) reveal the underlying mechanisms that produce the sex binary.

But they also reveal why the sexes are fundamentally defined by the reproductive structures that support either gamete type, and not chromosomes. Visit our website for the full gallery of sex development charts.
theparadoxinstitute.com/read/sex-devel…

This sex spectrum thread follows the exact, mind-numbing formula of “look at all this variation” without understanding 1) the difference between variation and disorder and 2) the biological definition of sex.

The sexes are not chromosomes.

https://twitter.com/bschillace/status/1641055339846959105

Sexes are phenotypes (body structures) that produce two different gamete types. Males develop towards the production of sperm, and females develop towards the production of eggs.

That’s why we can define someone with XXY as male because sexes are defined by gamete type.

Our professional prints of the “Myths of Gender Affirming Care” pamphlet arrived!

Photos below.

Gender activists think that a flamingo turning pink because of its diet is an example of a phenotype change detached completely from genes.

But without the genetic ability to convert and store the carotenoids they ingest, they would not turn pink. While phenotype can be influenced by additional factors outside of just the genotype, such as diet, stress, and other circumstances, phenotype is *always* influenced and regulated by genotype, even when the initial trigger for the change is environmental.

Understanding the function of a system is a cornerstone of biology and medicine.

It does not mean, as gender activists claim, that describing function necessarily implies a metaphysical designer (i.e. God).

Philosophers of Biology have been discussing this for a long time. [1] Neander, K. (1991). The teleological notion of 'function.' Australasian Journal of Philosophy, 69(4), 454-468.

.@PTElephant has a message to share regarding the conversation about Dylan Mulvaney between @buttonslives and @BillboardChris. Below is some of the context for those wondering what exactly Cynthia is responding to.

We need to eliminate the legal fiction of gender identity based sex markers.

You should be able to get hormones and surgery for your trans identity as an adult, but you should not be able to change your sex marker. This is so that sex-based protections can be upheld in the law. There are relevant and irrelevant situations for people knowing your sex.

Your ID should list the biological traits that identify you, such as height, weight, eye color, hair color, and your sex.

These traits are looked for on your ID when relevant, not in every situation.

People thinking Neil DeGrasse Tyson owned Ben Shapiro here really shows how uninformed they are.

Neil argues that if we just divide sports by hormone categories, that would cover any unfair advantages regarding trans women.

But men and women are not hormone levels.

https://twitter.com/aridrennen/status/1636820742888366080

Reducing hormone levels does not eliminate male advantage, because men’s and women’s bodies are organized differently through development and exposure to incredibly different hormone levels over time.

I am avidly against Scott and his beliefs.

I do not support spreading fabricated photos of political opponents.

It weakens your argument, it makes people less likely to believe what you're saying, and it's also a great way to open yourself up to defamation suits 😋

https://twitter.com/thegaywhostrayd/status/1636765547378675714

The photoshop was created by Jaimee Michell, the GAG founder.

https://twitter.com/thegaywhostrayd/status/1636454897087397888?s=20

Disentangling the use of the terms “sex” and “gender” will be critical for clarity in research papers on sex differences going forward. Many papers I cited in my books used the term “gender” as a synonym with sex. I even used the term “gender differences” to describe behavioral and psychological sex differences.