History of the Universe and Earth

[PutraenusAlivius]

Time for to temporarily change the topic to the History of the Earth.

Spoiler below!

HISTORY OF THE EARTH
TOPIC: CHROMOSOMES

MISSING CHROMOSOME PAIR
Do you guys know the Primate Genome project?

If you don't, it's about sequencing the primate genome to something.

Anyways, when the results came back, they compared the Human genome, yes our genome, to the results.

The study shows that all primates have 48 pairs of Chromosomes, while Humans have 46.

Where did this chromosome pair go? Did it went lost? If so, then it's fatal as even if one chromosome is lost, the whole stuff goes broken.

Researchers is founding the lost chromosomes. Guess what? They merged into a single chromosome.

Guess what chromosome it is? Aaand it's Chromosome number 2.



This is the chromatid for Chromosome 2.

You guys probably won't see this, probably because it's just a concept, but there's more evidence supporting this.

A chromosome usually have 2 telomeres at the end and a single Centromere right?

Well there's a vestigial Telomere at the middle, supporting an end-to-end fusion.
There is also a vestigial Centromere too.
So, Chromosome 2 is unique to humans because it came from two fused primate chromosomes.

DEGENERATION OF THE Y CHROMOSOME

There is two sex chromosomes which are the X and Y chromosome with the Y choosing the gender. XX means 2 X chromosomes which means a female. But XY means one X and one Y chromosome, which leads to a male.



The X has more than 153 million base pairs and represents 2000 out of 20000 - 25000 genes.

But the Y has 50 million base pairs, but Y controls the gender.

A study shows that along the course of Human evolution, the Y chromosome lost 1.393 of it's original 1.438 genes.

This is because:
- The Y chromosome is unable to recombine with other chromosomes during Meiosis
- It has a genetic drift meaning that the Y chromosome only has a 1/4 chance of being passed down
- It has a high mutation risk and therefore parasites can latch on

So, during the last stages of the Y chromosome's degeneration, other genes take over some things that was associated with the Y chromosome and a new sex determining system arises.

Tokudaia spp. is an example of this. This species has entirely lost the Y chromosome and SRY. But, some genes that was ancestrally present on the Y chromosome is now on the X chromosome.

And that's all I got.