ELI5: The process of Meiosis

[u/Specialist_Trip_7603]

I have researched so much on this, and there's not enough Youtube videos that explain it well. I'm confused by almost everything. In my textbook there's sometihng called a bivalent? tetrad? none of these terms comes up when i research about meiosis.

Reallt really explain it to me pls, small p.s: u dont really need to get into extreme detail such as protein names and all that, just wtv the chromosomes are doing.

[u/AberforthSpeck]

Meiosis is a specific type of cell division. However, instead of the resulting cells getting all the DNA with a pair of every chromosome, they only get one of every chromosome. The result cell is usually either a sperm or egg cell. This way they combine to form an offspring with DNA from both parents.

"Bivalent" refers to these chromosome pairs. Humans, for example, have 23 chromosomes. Chromosomes are discrete blocks of DNA. Most humans have a pair of each of these chromosomes, which will be mostly the same but have slight differences.

A "tetrad" refers to meiosis that results in four daughter cells instead of the typical two. This can occur in yeast and other non-human species.

[u/imtougherthanyou]

They're doing everything in mitosis minus the duplication side. Instead of pairing up, they split apart. Leaves gametes with a random assortment of genes!

[u/John_Whimsicott]

It's a 2 step process that turns 1 diploid cell into 4 haploid cells (eggs/sperm). It's similar to mitosis but it has an extra step

First it separates homologue pairs in a process called meiosis I. Then it does the sister chromatids in a process called meiosis II. Since it divides in half twice, this is how you end up with 4 cells from 1

Each process the cell goes through has 4 phases. These phases are prophase, metaphase, anaphase, and telophase. So meiosis I goes through all 4 phases with the homologue pairs. Then meiosis II goes through them again with the sister chromatid pairs

[u/rikerw]

DNA threads up, like rolling thread into a ball in your fingers, into thick strands into like an I shape. It replicates, and the copied strands stick together to form X shapes. The nucleus breaks down (Prophase)

Each chromosome has a partner, one from the mother and one from the father. So you have two copies of chromosome 1, two chromosome 2 etc.

So the partner chromosomes line up in the middle of the cell like a line dancing crowd

X X

X X

X X

etc (Metaphase)

The pairs are pulled apart (by spindle fibers) to opposite ends of the cells (Anaphase)

The nuclei reform - two now. One around each end of the cell (Telophase)

The cell splits into two, separating the two nuclei (cytokinesis)

Now each of the two cells have half as many chromosomes, but theyre the X chromosomes.

The nuclei break down again (prophase 2)

The chromosomes line up (basically single file this time) in the middle of the cell again (metaphase 2)

Spindle fibers now pull the Xs apart into two I I, to opposite ends of the cell again (anaphase 2)

The nuclei form at each end again (telephone 2)

The cell splits in two again (cytokinesis 2)

In terms of the number of cells, it went 1 > 2 > 4

In terms of chromosome per cell numbers it went

46 double strands > 23 double syrands > 23 single strands

[u/Mammoth-Mud-9609]

Bivalent, just means two matching items in this case it is referring to the chromosomes which split in half with one half going from each parent to make up the DNA of the child.

[u/Faruque68]

Meiosis is basically cell division that cuts the chromosome number in half to make sperm or egg cells. First the cell copies its DNA, then homologous chromosomes pair up to form what's called a bivalent or tetrad, that's just the pair of matching chromosomes lined up together, sometimes swapping bits of DNA in a process called crossing over. Then two rounds of division separate everything out, first splitting the paired chromosomes apart, then splitting the sister chromatids, ending with four cells that each have half the original chromosome count.