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The secrets of the X chromosome. These women are identical twins. They have the same nose, the same hair color, the same eye color. But this one is color blind
for green light, and this one isn’t. How is that possible? The answer lies in their genes. For humans, the genetic information
that determines our physical traits is stored in 23 pairs of chromosomes
in the nucleus of every cell. These chromosomes are made up of proteins
and long, coiled strands of DNA. Segments of DNA, called genes,
tell the cell to build specific proteins, which control its identity and function. For every chromosome pair,
one comes from each biological parent. In 22 of these pairs, the chromosomes
contain the same set of genes, but may have different versions
of those genes. The differences arrive from mutations, which are changes to the genetic sequence that may have occurred
many generations ago. Some of those changes have no effect, some cause diseases, and some lead to advantageous adaptations. The result of having two versions
of each gene is that you display a combination
of your biological parents’ traits. But the 23rd pair is unique, and that’s the secret behind
the one color blind twin. This pair, called the X and Y chromosomes,
influences your biological sex. Most women have two X chromosomes while most men have one X and one Y. The Y chromosome contains genes
for male development and fertility. The X chromosome, on the other hand, contains important genes for things other
than sex determination or reproduction, like nervous system development, skeletal muscle function, and the receptors in the eyes
that detect green light. Biological males with
an XY chromosome pair only get one copy of all these
X chromosome genes, so the human body has evolved
to function without duplicates. But that creates a problem
for people with two X chromosomes. If both X chromosomes produced proteins,
as is normal in other chromosomes, development of the embryo would be
completely impaired. The solution is X inactivation. This happens early in development
when an embryo with two X chromosomes is just a ball of cells. Each cell inactivates one X chromosome. There’s a certain degree of randomness
to this process. One cell may inactivate the X chromosome
from one parent, and another the chromosome
from the other parent. The inactive X shrivels into a clump
called a Barr body and goes silent. Almost none of its genes
order proteins to be made. When these early cells divide,
each passes on its X inactivation. So some clusters of cells
express the maternal X chromosome, while others express the paternal X. If these chromosomes
carry different traits, those differences
will show up in the cells. This is why calico cats have patches. One X had a gene for orange fur
and the other had a gene for black fur. The pattern of the coat reveals
which one stayed active where. Now we can explain our color blind twin. Both sisters inherited one mutant copy
of the green receptor gene and one normally functioning copy. The embryo split into twins
before X inactivation, so each twin ended up
with a different inactivation pattern. In one, the X chromosome
with the normal gene was turned off in the cells that eventually became eyes. Without those genetic instructions, she now can’t sense green light
and is color blind. Disorders that are associated
with mutations of X chromosome genes, like color blindness, or hemophilia, are often less severe in individuals
with two X chromosomes. That’s because in someone with one normal
and one mutant copy of the gene, only some of their cells would be
affected by the mutation. This severity of the disorder
depends on which X got turned off and where those cells were. On the other hand, all the cells in
someone with only one X chromosome can only express the mutant copy
of the gene if that’s what they inherited. There are still unresolved questions
about X inactivation, like how some genes on the X chromosome
escape inactivation and why inactivation isn’t always random. What we do know is that this mechanism is one of the many ways that genes
alone don’t tell our whole story.

James Carver

100 Replies to “Secrets of the X chromosome – Robin Ball”

  1. she has a slight … I dont know how to explain it but it erks the fuck out of me. its almost like she has too much saliva in her mouth

    I mean no offense but male announcer, where you at fam ✌

  2. Inactivation is mostly random in all chromosome not just x(not all genes are accumulative) and parts of both chromosome inactivate not only one(but for explanation the description given is fine since it amount to the same thing). The father has to have color blindness and the mother at least one x chromosome for the the daughter to have it. The difference is more likely a mutation occurring later in development or environmental factors.

  3. What do you mean when you said "most" men have an X and Y chromosome and "most" women have 2 X chromosomes? Are there cases where "XY" = male and "XX" = female are not the case? If so, can you explain?

  4. This is a brilliantly developed video! The explanation is clear and engaging of such complex topic, and the visual resources also allow a perfect understanding of the verbal explanation. I always enjoy watching your channel, congratulations TED-Ed!

  5. not most women have X and most males have Y, irs is ALL you cannot be the opposite gender of your chromosome, then you'd be that gender duh

  6. Guys I have a question regarding about X inactivation and Turner Syndrome.
    Why do females with Turner syndrome have developmental abnormalities, when normal XX females do not, even though they only have 1 active X chromosome? From what the video has discussed, one X chromosome is inactivated/silenced and turns into a Barr body in normal XX females but these obviously don't show the symptoms of Turner syndrome.

  7. great video as always!

    oh also, the presenter never said "gender" (or i didn't hear it). i am surprised how controversial the word has become.

  8. i have a question. what about carrier (women carrying heterozygous color blind genes)? from what i learned, most carrier are normal. but according to this video, there are chance for carrier to have color blind phenotypes.

  9. I didn't understand one thing that if one x chromosome is inactivated then how can a female be normal but a carrier?

  10. I especially love the ending because the short information on mutations such as hemophilia really help connect the specific subject to something that happened because of inbreeding in European royalty. I remember reading a really fascinating insight into the fact that many princes born into royalty suffered from the Royal Disease (the inability to clot) and their sisters rarely had to deal with the same problem because of their two X chromosomes.

  11. I m a med student and i found this explanation excellent…so complex and confusing topic explained in such a simplified way…Ted ed is by far best youtube channel but its scary to see 35 million subsrcibers on justin bieber channel and just 5 on such an excellent educative channel…whats our population upto…no doubt we are loosing our intellect and thirst for knowledge with time..!!

  12. This is fascinating for me as someone who has Incontinentia Pigmenti. This actually explains why my genetic disorder is not as severe as others because the cells that have the mutated X chromosome only manifested by my feet. If it had been on my chest, it would have affected my breathing. And I never understood why. Now I know.

  13. 3:37 the embryon divide into 2 cells before X inactivation So each twin will inactivate an X differentely (in one cell the chromosome with normal gene will turned off and in the other cell the oppposite case ) but after this the two cells will be divide so they can an other time activate either the normal chromosom or the mutant chromosome !!!!! please someone explain to me in english or french

  14. At 0:57, can anyone explain what do they mean by "in 22 of these pairs, the chromosomes contain the same set of genes" ?All the 22 pairs have the same gene which differ only in alleles?

  15. Don't you just love genetics! Sooo fascinating. When breeding Doberman Pinchers & other breeds, every good breeder would have their breeding stock tested for VonWillibrants Bleeding disorder.

  16. I wish they had subtitles in english for these vedios .Because they cover such amazing topics in short time ,they speak fast n its hard to memorize these things.
    Inspite of being
    so amazing they do vry little gud to me.

  17. Pls tedEd do this for me i would really appreciate if u fulfill my whish.just make little notes of wht u say so that i could screen shot them.

  18. Even though they don’t really go into detail about some of the process (such as X inactivation) I really like how the video was done. It broke down most of the process fairly succinctly and introduced the perspective audience to a wide range of topics within this spectrum. Also love the use of the word “most” in the context of X and Y chromosomes

  19. If xx chromosome is male and xy is female wheres the genetic makeup for these made up feminazi faggots? 😂😂

  20. the biological purpose of the male is to MAKE A BETTER FEMALE. the default organism is female. patriarchy does everything it possibly can to "reverse" this truth by stating the opposite.

  21. I think that epigenetics has something to do with why some genes, on the inactivated x chromosome, escape x-inactivation. I don't know but I think I'm right.

  22. I find it funny how the creator of the video has chosen to use a girl as an example in which case someone is colorblind. Girls are rarely affected by the gene of color blindness while boys are more likely to have it. A girl can only get it when both of her parents have the gene for for it. Otherwise, I find it odd how she mentions that an individual with two X-chromosomes “often” is the gender of a female. An individual who has two X-chromosomes is and will always be a girl.

  23. I remember when I was younger, my classmate once asked the teacher, “Why do girls have more genes?” The teacher groaned. “Why?” the teacher asked. “Because they need more pairs for their shirts!” he said. The teacher than gave him a minus on his work.

  24. 🤔So The X Chromosomes Are Like A Bingo Wheel Or Slot Machine, Just Never Know Which And You Just Never Know When. That's A Cool Imagery.
    Ooooh Now From The Kitty, You Can See Which Active Parent Gene Divided In The Direction.🙊

    Imma Have To Come Back And Re Watch This Video After Some Further Research I Couldn't Follow To Well. This Video Was Enlightening.

    Wait Could This Be Where Polar Opposite Twins Come From?!🙊

  25. WonderfuI explaination….however I have a question…then why tuners get affected if all women need one X gene for functioning…???

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