If men have XY and women have XX, what would happen if scientists created a YY human?

A person with two Y chromosomes and no X chromosome is biologically impossible, because the X chromosome is essential in order for your organs to form correctly. If a person were conceived with two Y chromosomes and no X chromosomes whatsoever, that person would probably die in the womb as a miscarriage. You can live without a Y chromosome. (I’ve been doing it for over twenty-two years!) You can’t live without an X chromosome.

The default sex for every human being is female. The only thing the Y chromosome is good for is turning people who would otherwise be totally female into men. That’s literally all it’s good for. The X chromosome, by contrast, is the one with all the vital organ-building information, including information on how to form organs unrelated to sexual reproduction. The X chromosome is a bit like your heart: everyone needs one and everyone who’s alive has at least one.

That’s also why the Y chromosome is absurdly tiny. It’s not even half the size of the X chromosome because it has to carry way less genetic information. The X chromosome carries 155 million base pairs and 804 known genes, but the Y chromosome only carries fifty-nine million base pairs and only sixty-three known genes:

Technically speaking, men and women actually have the same organs; the Y chromosome just causes those organs to form differently in males. You see, sex is genetically determined at conception, but, in the first few weeks after conception, the embryo has no anatomical or hormonal sex. You can’t tell a male zygote from a female zygote by looking at it. It’s what we call “undifferentiated.”

An undifferentiated male embryo basically develops as it would if it had no Y chromosome and is indistinguishable from a female embryo at the same stage of development. They both have a generic set of undifferentiated genitalia that can develop into either male sex organs or female sex organs (or the process can sometimes go differently from normal and the infant can end up with neither male nor female sex organs, but those cases are generally pretty rare).

Eventually, after the first few weeks, the Y chromosome kicks in in males and they start to develop male primary sex characteristics, such as a penis and testicles. Meanwhile, females continue to develop without the Y chromosome, causing them to develop a uterus, ovaries, a vagina, and a vulva. Here’s a diagram showing human sex differentiation:

As a result of this, male and female sex organs are homologous to each other. The penis is homologous to the clitoris. The foreskin is homologous to the clitoral hood. The scrotum is homologous to the labia majora. The scrotal raphe is homologous to the labia minora. The testes are homologous to the ovaries. The appendices of the testes are homologous to the fallopian tubes. The prostatic utricle is homologous to the vagina, cervix, and uterus. (Sorry men, I guess you all technically sort of have pussies.) The prostate is homologous to Skene’s glands. (You’ve probably all at least heard of female ejaculation, right? The fluid that’s ejaculated is probably produced by Skene’s glands.)

The fact that males and females start out development the same is probably one of the main reasons why adult males actually produce low levels of the female hormones estrogen and progesterone and adult females produce low levels of the male hormone testosterone. Even as adults, we’ve all still got a bit of the other gender left in us.

The only reason why men are men and not women is because of the Y chromosome. The thing is, the Y chromosome only works if you also have an X chromosome, because the Y chromosome essentially just modifies the genes carried by your other chromosomes, including the X chromosome. Without the X chromosome, the Y chromosome is basically useless. It’s sort of like how wearing glasses is useless if you don’t have eyes. That’s why scientists would never be able to create a person with two Y chromosomes and no X chromosome.

In any case, there would probably be no benefit to having a second Y chromosome anyway, because having two of the same chromosome generally doesn’t have much of an impact. Women usually have two X chromosomes, but very early in fetal development, one of those X chromosomes in every cell is inactivated. Again, the X chromosome is kind of like your heart: you need one to live, but you only really need one and having a second one is mostly just redundant. (Sorry Time Lords!)

There are some men who have one X chromosome and two Y chromosomes. Usually, all that happens with the second Y chromosome is the exact same thing that happens to women’s second X chromosome: it just shrivels up and goes dormant while the other acts as the dominant one.

This information was taken from Quora. Click here to view the original post.

Have you ever wondered why we can't have the YY pack of chromosomes? Did you know that the default sex for every fetus is always female?

#Science #Quora


What are your thoughts on this subject?
Simon Morris
2 Ys U R 2 Ys U B, I C U R 2Ys 4 Me.
Apr 5, 2019 10:32PM
So, it should be called the "why" chromosome then? Since we only need men to produce MORE men, technically, this world could be a very peaceful place. No wonder they are so touchy. If I knew that I literally had only one unique (although not necessary otherwise) purpose, I'd be touchy too.
May 2, 2019 1:45PM
Jaimi McEntire
Palmer Scott, Vicky mention XYY males, not XXY males (Kleinfelter syndrom). XXY males are not more aggressive, but XYY males are prone to be taller and have behavioral issues and learning disabilities.
Jan 25, 2023 5:32PM
Interesting. Keep it coming QC. I am learning so much!
Jan 15, 2023 12:54AM
Michael Garmaise
Vicki Cane, NOT TRUE!
Dec 19, 2022 6:15PM
Palmer Scott
Vicki Cane, no, XXY males are not inherently more aggressive and found in prison. And XXY males are not all sterile.
Nov 3, 2022 5:30PM
Palmer Scott
Cindy Schaub, please read a bit before making such a comment. There are XYY and XXY males, as there are XXY females. Genetics is a lot more complicated than just XX and XY!
Nov 3, 2022 5:28PM
Fred Mayes
bipolarintrovert, well, you need men to make women, as well.
Sep 11, 2022 9:34PM
Jan Ashbaugh
So we women really do rule the world!!
Apr 24, 2022 12:44PM
Karen W
Never knew this, interesting info!
Apr 21, 2022 9:09PM
Cindy Schaub
dawnbartlett, There can not be a second Y chromosome. the egg would never develop into a fetus if there were a 2 Y chromosomes. No X = No organs and there are only 2 chromosomes. It can't be YYX - it can only be XX or XY.
Mar 5, 2021 7:34AM
Actually a second Y chromosome in men can make them violent and dysfunctional so much so that they usually end up in prison
Jul 8, 2020 1:02AM
James Bailey
Habakuk Capek, genetically? They don't.
Nov 5, 2019 7:45PM
Kimberley Wood
Females do not carry Y chromosomes so it is impossible to have a YY baby. Men produce both X sperm and Y sperm so the theory of having one X chromosome in women being dormant and the other dominant is absurd. Females need both X chromosomes to be female! In females of all species, one X chromosome comes from the mother and the other comes from the father. In males, the X chromosome comes from the mother and the Y chromosome comes from the father. Again, this is because adult males produce both X and Y sperm. If an adult male produced only X sperm then all of his offspring will be female and if an adult male produced only Y sperm then all of his offspring will be male. There have been reported cases around the world where men have produced sperm of only one chromosome (X or Y).
Sep 4, 2019 7:02PM
Vicki Cane
If someone is an XYY it’s called a “super male” and the vast majority are found in the prison system, so not redundant and of no effect. And an XXY is infertile ( Kleinfelter male), As is an XO or Turner female.
Jul 16, 2019 8:14PM
Lu-Anne Murdoch Anderson
I did know that we all start out as females. Very informative.
Jul 15, 2019 1:53AM
hector tubens
Very interesting information.
Jun 29, 2019 8:46PM

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