Veritasium
2 HN recommenders · recommended in 4 months, 2015–2026
5:17 · 11M views · Jun 4, 2014
Veritasium explains X-chromosome inactivation, where different cells in a woman's body switch off different X chromosomes, giving a mosaic pattern. It uses animation from the WEHI institute and connects to calico cat coloring.
Commenters point to it as the best short explanation of X inactivation and why calico cats and some human traits are mosaics.
5 comments from Hacker News
This is only tangentially related, but Veritasium has a fantastic video that discusses the genetics behind the random color patterns of calico cats: this video
The next article in this series on "Which sex is playing higher stakes reproductive game?" is also worth reading: [LINK] It reminds me of an interesting hypothesis I've read about the other day that the concept marriage plays a significant role in the success of our culture as it counteracts this difference. It allows more men to reach a social status at which they are motivated to be productive members of society. So we are possibly actively destroying a pillar of our culture as we are devaluing marriage. By the way, Veritasium has a great episode on why women are stripey: this video
This to me looks like the "very small number" refers to the ones where this is visible, not to the amount of them that has somewhere mosaic-style cell patterns. For example it is widely known now that if not most women, all women have mosaic patterns on their retina, this not only explains differences in disabilities (like the ocular albinism in the article, but also daltonism), but in perception: While men can see 3 primary colours, women can see 6, it is of course 2 kinds of each other, but still 6, this might explain why women treat colour differently than men (example: women are more interested in the colour of home decoration and clothes, they give more names to colours than men do, they can choose between two very similar nail polish colours when most men don't notice the difference, and so on). Why is that of course veers in the theoretical, the best guess is that while men is better to track motion, probably because they were the primary hunters, women are better in dealing with other types of food (for example colour is important to figure how good to eat vegetables are... there is a reason why farming corporations improve the colour and shape of their fruits, instead of improving the taste). EDIT: someone posted a video elsewhere on the thread about this subject: this video
I assume it is the same reason that women have stripey skin. at ~ 100 cells, if the embryo has 2 X chromosomes the cell shuts one of them off, which one is random, those cells continue to multiply bringing their specific X chromosome with them. So women have genetically distinct blotches all over their body based on which cell disabled which X chromosome. I will have to leave this one for the scientists but I assume tetracromats got some of their cone cells from X and the rest from X` this video (veritasium: Why Women Are Stripey) The implication being, I don't think tetracromats have some sort of super vision, they just have what would be considered color blind if all their color cells were defective. But because only some of them are they get an interesting subtle addition to their color sense.
Human women have stripey skin too, but you can't see it under normal light because unlike cats, skin tone in humans is not controlled by the X chromosome. this video