the chromosomes that determine sex?

Question

Could someone explain what the y and x chromosome are, what part they play in our biology and how they determine our sex? I hear this topic come up a lot and I have no idea what they are. Doesn’t an extra chromosome also mean a person might have down syndrome? Thanks guys.
(Not looking for a political debate btw, just straight biology, thank you)

In: 4

Answer 1

DNA is a string-like chemical that exists in each and every one of your cells (except red blood cells). I can take a hair follicle or a bit of skin or some extra tissue from the inside of your cheek, and that small amount is enough for me to get a copy of all of your DNA.

Each of your cells as 46 strings of DNA. When it comes time for a cell to replicate, all that DNA is duplicated, then it wraps up tightly (imagine twisting a string until it folds on itself, then twisting the fold until *that* folds on itself, etc.) until you get these big X-shaped DNA knots called chromosomes. Then the cell splits in two, and the DNA unravels again.

Here’s a (https://www.youtube.com/watch?v=L0k-enzoeOM) of that happening.

So you have 23 unique chromosomes, but you have 2 copies of each. One from mom and one from dad. Chromosomes 1 through 22 are just named after numbers. If you have three chromosome 21s, that’s what Down’s syndrome is. If you have three chromosome 18s, that’s what Edward’s syndrome is. The 23rd chromosome comes in two varieties, X and Y, and we don’t call them chromosome 23.

So mom has two X chromosomes. That means, no matter what, she gives the child an X chromosome. Dad, on the other hand, has an X and a Y. So when he gives you half of his genes, there’s a 50% chance he gives you an X and a 50% chance he gives you a Y.

On the Y chromosome, there is a gene called the SRY gene. Occasionally the SRY gene gets broken off and put on the wrong chromosome, but for the most part it’s on the Y chromosome. If you get an SRY gene, you’ll be a dude (most of the time) and if you don’t, you’ll be a girl (most of the time). So that’s why XY is male and XX is female.

If you want to have a deeper understanding, just watch all the crash course biology episodes on youtube.