The Y chromosome doesn’t carry much of anything. It’s basically just a carrier for the SRY gene, and in most cases, it’s that gene that triggers the majority of the sexual differentiation that occurs in early development. The actual “code” for what develops and how it develops is there for male and female differentiation in all humans, and it’s hormones and other factors that control whether or not that genetic code is expressed.
And in this case, we’re talking about stem cells (ie, a cell that has the potential to develop in to any cell, but hasn’t yet done so), and then artificially triggering those stem cell to develop in to sperm cells. A trick that can be done because the genetic code for it to do so is already there if the conditions are right.
As an aside, this is also why hormone replacement for trans people lets them develop secondary sexual characteristics that they wouldn’t otherwise develop. The code was already there, it just takes the right trigger to get the code expressing (in this case, hormones)
The Y chromosome does a bit more than just carry the SRY gene.
There is a condition where a father’s SRY gene gets transfered to the X chromosome of a sperm, resulting in a child who is XX and SRY positive. [0]
In all known cases, such men are infertile. Fertility treatment is the main source of diagnoses for this, as that is typically the only symptom.
[0] This is de la Chapelle syndrome, although that syndrome also covers an even rarer situation of an XX SRY-negative child developing as a male.
There is also Swyer syndrome where an XY individual develops as a female (typically due to a defact in SRY). Such individuals general do not go through natural puberty and require hormone therapy.
until now, I always assumed that genes for sperm were on the Y chromosome, but I guess they’re not?
The Y chromosome doesn’t carry much of anything. It’s basically just a carrier for the SRY gene, and in most cases, it’s that gene that triggers the majority of the sexual differentiation that occurs in early development. The actual “code” for what develops and how it develops is there for male and female differentiation in all humans, and it’s hormones and other factors that control whether or not that genetic code is expressed.
And in this case, we’re talking about stem cells (ie, a cell that has the potential to develop in to any cell, but hasn’t yet done so), and then artificially triggering those stem cell to develop in to sperm cells. A trick that can be done because the genetic code for it to do so is already there if the conditions are right.
As an aside, this is also why hormone replacement for trans people lets them develop secondary sexual characteristics that they wouldn’t otherwise develop. The code was already there, it just takes the right trigger to get the code expressing (in this case, hormones)
So you’re telling me that somewhere in my biological code is my mom’s tits. And if I just take some estrogen, I can have my mom’s tits?
Your dad’s tits are there too. You might get his.
The Y chromosome does a bit more than just carry the SRY gene.
There is a condition where a father’s SRY gene gets transfered to the X chromosome of a sperm, resulting in a child who is XX and SRY positive. [0]
In all known cases, such men are infertile. Fertility treatment is the main source of diagnoses for this, as that is typically the only symptom.
[0] This is de la Chapelle syndrome, although that syndrome also covers an even rarer situation of an XX SRY-negative child developing as a male.
There is also Swyer syndrome where an XY individual develops as a female (typically due to a defact in SRY). Such individuals general do not go through natural puberty and require hormone therapy.