I'm sorry
@Sarah B but this is part of the problem.
You have taken one set of biological markers and excluded so many others. We already know that there are intersex states, which you haven't mentioned despite some members on here having been born intersex. Intersex is one illustration of why you cannot slap binary assignation on individuals without understanding the complexities involved.
There are also a huge range of other "Biological sex" markers that are deliberately ignored as part of a trans exclusionary agenda.
These include, but are not limited to, chromosome variations, alleles, receptors, aromatase, neurons and neural plasticity, hydroxylation, astrocytes, hormone ranges and hormone endocrines (which are never tested at birth), brain signals and receptors including the pituitary gland and the hypothalamus, mental congruence and incongruence etc. etc. the list is almost endless and complex, never tested at birth for variance and (of course) some of this variation develops later into what some people delineate as gender incongruence. But gender incongruence rarely occurs in a vacuum. It can have environmental triggers (nurture) but even these are almost always rooted in antecedent biological markers (nature)
which are every bit as much a part of biological sex .
There's plenty of evidence that hormone differences, for example, can be incongruent with external genitalia just as brain function can be incongruent with the bodily presentation. That's not just a lesser 'gender'. It's bound up with biological sex. You cannot separate them without descending into reductionism, which is never a good thing. You cannot separate out one part of the bodily function from others and say, in true reductionist fashion, that
this is the defining characteristic. It's this sort of casual acceptance which, for example, leads people to assume that mental ill-health is somehow not related to physicality. That somehow the brain exists in a vat.
@KathyLauren is correct and, with respect, our community has made a mistake in letting this lazy adoption of the term 'biological sex' (mostly by non-medics by the way) to be stamped without greater understanding of the complexities of sex and gender. This is an age where nuance is sacrificed to understanding. Don't let this place go that way too.
Throughout my childhood my mother used to joke that she thought my chromosomes must have been mixed up. As it happens over 50 years later during some blood testing they discovered that I do, indeed, have a chromosome mutation (they prefer the term 'variance' now). That chromosome mutation was never tested at my birth, so the body with which I was assigned was incongruent. That's
biological ...
Not gender. Sex. Wrongly labelled. Because like most binary thinking, and most labelling, it's simplistic. And simplistically wrong.
xx
Almeida M, Laurent MR, Dubois V, et al. Estrogens and androgens in skeletal physiology and pathophysiology. Physiol Rev. 2017;97(1):135–187. doi: 10.1152/physrev.00033.2
Beery AK, Zucker I. Sex bias in neuroscience and biomedical research. Neurosci Biobehav Rev. 2011;35(3):565–572. doi: 10.1016/j.neubiorev.2010.07.002
Kaczkurkin AN, Raznahan A, Satterthwaite TD. Sex differences in the developing brain: insights from multimodal neuroimaging. Neuropsychopharmacology. 2019;44(1):71–85. doi: 10.1038/s41386-018-0111-z
Rigby N, Kulathinal RJ. Genetic architecture of sexual dimorphism in humans. J Cell Physiol. 2015;230(10):2304–2310. doi: 10.1002/jcp.2497
Boucher and Chinnah 2000 'Gender Dysphoria: A Review Investigating the Relationship Between Genetic Influences and Brain Development'
https://pmc.ncbi.nlm.nih.gov/articles/PMC7415463/ 🔗Hoekzema E, Schagen SEE, Kreukels BPC, et al. Regional volumes and spatial volumetric distribution of gray matter in the gender dysphoric brain. Psychoneuroendocrinology. 2015;55:59–71. doi: 10.1016/j.psyneuen.2015.01.016
Burke SM, Cohen-Kettenis PT, Veltman DJ, Klink DT, Bakker J. Hypothalamic response to the chemo-signal androstadienone in gender dysphoric children and adolescents. Front Endocrinol. 2014;5:60. doi: 10.3389/fendo.2014.00060
Luyckx K, Schwartz SJ, Goossens L, Beyers W, Missotten L. Processes of personal identity formation and evaluation In: Handbook of Identity Theory and Research. 2011:77–98. doi: 10.1007/978-1-4419-7988-9_4
Hannema SE, Print CG, Charnock-Jones DS, Coleman N, Hughes IA. Changes in gene expression during Wolffian duct development. Horm Res. 2006;65(4):200–209. doi: 10.1159/000092408
Sekido R, Lovell-Badge R. Sex determination involves synergistic action of SRY and SF1 on a specific Sox9 enhancer. Nature. 2008;453(7197):930–934. doi: 10.1038/nature06944
Morel Y, Roucher F, Mallet D, Plotton I. Genetic of gonadal determination. Ann Endocrinol. 2014;75(2):32–39. doi: 10.1016/j.ando.2014.04.005
Ohnesorg T, Vilain E, Sinclair AH. The genetics of disorders of sex development in humans. Sex Dev. 2014;8(5):262–272. doi: 10.1159/000357956
Parma P, Radi O, Vidal V, et al. R-spondin1 is essential in sex determination, skin differentiation and malignancy. Nat Genet. 2006;38(11):1304–1309. doi: 10.1038/ng190
Luders E, Toga AW. Sex differences in brain anatomy In: Progress in Brain Research. 2010:2–12. doi: 10.1016/B978-0-444-53630-3.00001-4
De Bellis MD. Sex differences in brain maturation during childhood and adolescence. Cereb Cortex. 2001;11(6):552–557. doi: 10.1093/cercor/11.6.552
D'Andrea S, Pallotti F, Senofonte G, et al. Polymorphic cytosine-adenine-guanine repeat length of androgen receptor gene and gender incongruence in trans women: a systematic review and meta-analysis of case-control studies. J Sex Med. 2020;17(3):543–550. doi: 10.1016/j.jsxm.2019.12.010
Claas Flint, Katharina Förster, Sophie A. Koser, Carsten Konrad, Pienie Zwitserlood, Klaus Berger, Marco Hermesdorf, Tilo Kircher, Igor Nenadic, Axel Krug, Bernhard T. Baune, Katharina Dohm, Ronny Redlich, Nils Opel, Volker Arolt, Tim Hahn, Xiaoyi Jiang, Udo Dannlowski & Dominik Grotegerd 2020
'Biological sex classification with structural MRI data shows increased misclassification in transgender women'
Neuropsychopharmacology volume 45, pages1758–1765 (2020)
C E Roselli 2019 'Neurobiology of gender identity and sexual orientation' Neuroendocrinol. Author manuscript; available in PMC: 2019 Aug 2.
Published in final edited form as: J Neuroendocrinol. 2018 Jul;30(7):e12562. doi: 10.1111/jne.12562
Fernández R, Cortés-Cortés J, Esteva I, et al. The CYP17 MspA1 polymorphism and the gender dysphoria. J Sex Med. 2015;12(6):1329–1333. doi: 10.1111/jsm.12895
https://academic.oup.com/jcem/article/104/2/390/5104458 🔗Madeleine Foreman , Lauren Hare , Kate York , Kara Balakrishnan , Francisco J Sánchez , Fintan Harte , Jaco Erasmus , Eric Vilain , Vincent R Harley 2018 'Genetic Link Between Gender Dysphoria and Sex Hormone Signaling'The Journal of Clinical Endocrinology & Metabolism, Volume 104, Issue 2, February 2019, Pages 390–396,
https://doi.org/10.1210/jc.2018-01105 🔗Ritchie SJ, Cox SR, Shen X, et al. Sex differences in the adult human brain: evidence from 5216 UK biobank participants. Cereb Cortex. 2018;28(

:2959–2975. doi: 10.1093/cercor/bhy10
Ruigrok ANV, Salimi-Khorshidi G, Lai MC, et al. A meta-analysis of sex differences in human brain structure. Neurosci Biobehav Rev. 2014;39:34–50. doi: 10.1016/j.neubiorev.2013.12.004
Savic I, Berglund H, Gulyas B, Roland P. Smelling of odorous sex hormone-like compounds causes sex-differentiated hypothalamic activations in humans. Neuron. 2001;31(4):661–668. doi: 10.1016/S0896-6273(01)00390-7
Berglund H, Lindström P, Dhejne-Helmy C, Savic I. Male-to-female transsexuals show sex-atypical hypothalamus activation when smelling odorous steroids. Cereb Cortex. 2008;18(

:1900–1908. doi: 10.1093/cercor/bhm216
Sundermann EE, Tran M, Maki PM, Bondi MW. Sex differences in the association between apolipoprotein E ε4 allele and Alzheimer's disease markers. Alzheimer's Dement Diagnosis, Assess Dis Monit. 2018. 10:438–447. doi: 10.1016/j.dadm.2018.06.0