But the Chromosomes!!! 
⢠TransEthicsâ˘
#ProtectTransKids @TransEthics 
I'm going to regret paying the co-pay for this test eventually because it was pretty priceyâŚÂ but I had my karyotype done. Just got the results.
I âa trans womanâ have XX chromosomes.
the GC crowd can g[REDACTED]k themselves
Open Ocean Exploration @RebeccaRHelm 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 itâs so simple, letâs find the biological roots, shall we? Letâs talk about sex...[a thread]
Open Ocean Exploration @RebeccaRHelm If you know a bit about biology you will probably say that biological sex is caused by chromosomes, XX and youâre female, XY and youâre male. This is âchromosomal sexâ but is it âbiological sexâ? Well...
Open Ocean Exploration @RebeccaRHelm Turns out there is only ONE GENE on the Y chromosome that really matters to sex. Itâs called the SRY gene. During human embryonic development the SRY protein turns on male-associated genes. Having an SRY gene makes you âgenetically maleâ. But is this âbiological sexâ?
Open Ocean Exploration @RebeccaRHelm Sometimes that SRY gene pops off the Y chromosome and over to an X chromosome. Surprise! So now youâve got an X with an SRY and a Y without an SRY. What does this mean?
Open Ocean Exploration @RebeccaRHelm A Y with no SRY means physically youâre female, chromosomally youâre male (XY) and genetically youâre female (no SRY). An X with an SRY means youâre physically male, chromsomally female (XX) and genetically male (SRY). But biological sex is simple! There must be another answer...
Open Ocean Exploration @RebeccaRHelm 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 âbiological sexâ??
Open Ocean Exploration @RebeccaRHelm 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.
Open Ocean Exploration @RebeccaRHelm Biological sex is complicated. Before you discriminate against someone on the basis of âbiological sexâ & 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?
Open Ocean Exploration @RebeccaRHelm Of course you could try appealing to the numbers. âMost people are either male or femaleâ you say. Except that as a biologist professor I will tell you...
Open Ocean Exploration @RebeccaRHelm The reason I donât have my students look at their own chromosome in class is because people could learn that their chromosomal sex doesnât match their physical sex, and learning that in the middle of a 10-point assignment is JUST NOT THE TIME.
plant lesbian @alicemiriel @RebeccaRHelm As a fellow genetics lab teacher, this is the same reason my department stopped chromosome testing in lab. A really cool experiment would turn into guys getting freaked out they have XXY, etc.
There are dozens of ways that chromosomes can be much more complex than XX and XY. Medically these are referred to as DSDs (Disorders of Sex Development). Not all result in an intersex condition, and many only manifest at the onset of puberty.
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De la Chapelle Syndrome (46,XX Male) occurs when the SRY gene from the sperm parent crosses over into a non-Y-bearing sperm during spermatogenesis. When the egg and sperm merge, it results in an XX embryo with an SRY gene, creating a phenotypical male child with two X chromosomes.
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Swyer Syndrome (46,XY Female) produces a phenotypically female child with an XY chromosome. This results from a dozen different genetic conditions, including:
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XX Gonadal Dysgenesis is very similar to Swyer Syndrome, except occurs in XX children and results in nonfunctional ovaries.
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Turner Syndrome (45,X) produces a phenotypically female child with numerous abnormalities. It occurs when neither an X or Y chromosome crosses over from the sperm.
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Klinefelter Syndrome (47,XXY) results in a phenotypically male child with more feminine traits. In extremely rare cases it appears in female assigned children as well, resulting in feminized testicles instead of ovaries.
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49,XXXXY Klinefelter Syndrome is often fatal, but when it isnât, it will always results in a sterile child.
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Trisomy X (47,XXX), Tetrasomy X (48,XXXX), and Pentasomy X (49,XXXXX) all result in a female child, but with progressively more intense health issues.
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XXYY Syndrome results in male children (due to two SRY genes) which often experience hypogonadism, needing testosterone supplements, but otherwise seeming like a typical male
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Mosaicism results when some cells in the body have one set of chromosomes and other cells have another due to a mutation of the genome during gestation. This may be XX/XY (resulting in a dual set of genitalia), X/XY (a milder form of Swyer or Turner syndromes) or XX/XXY (a milder form of Klinefelter syndrome).
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Chimerism occurs when two fertilized embryos merge together into one zygote, causing half of the child to contain one set of DNA and the other half to contain another. This can result in an otherwise completely typical human being of either male or female phenotype, even capable of producing offspring, but which comes back on a kareotype test as not matching their phenotype based on where the sample was taken on their body. In extremely rare cases this can result in two full sets of reproductive organs.
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Congenital Adrenal Hyperplasia(CAH) is masculinization of the female genitals in an XX child due to overactive adrenal glands.
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Androgen Insensitivity Syndrome(AIS) is a total or partial resistance to all androgens, preventing masculinization of all organs, save for the testicles, in an XY child. AIS subjects typically develop a female gender identity, but some partial cases may be male.
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5-alpha-reductase deficiency(5ARD) is a failure in the bodyâs ability to metabolize testosterone into dihydrotestosterone (DHT), preventing masculinization of the genitalia until the onset of puberty, when the child suddenly grows a penis.
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Aromatase Deficiency causes masculinization of an otherwise female child due to excess levels of testosterone (and can bleed-over into the mother during gestation).
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Aromatase Excess causes feminization in an otherwise male child, as all testosterone is converted into estrogen.
