About Meiosis?

Question

Can someone tell me about meiosis 1 and 2? I get how in the first part, the diploid cell, becomes two haploids cells. But how the hell did two haploid cells become 4 OTHER haploid cells?
Thanks for your answer

Answer 1

a homologous pair of chromosome lie along side each other. each chromosone is also made up of two chromatids. and "crossing over" occurs ie. genetic material is exchanged between the chromatids.

when the nucleus devides for the first time, the chromosomes in a giving pair (not the chromatids) seperate and move to opposite ends of the cell. this results in only half the number of chromosomes going to each daughter cell.

during the second nuclear division, the chromatids separate and move to opposite ends of the each daughter cell. this gives rise to four gamete cells, each with a haploid number of chromosome.

Answer 2

The point of meiosis I is to get the pairs of homologous chromosomes away from each other.
-- The homologous chromosomes match up together and form tetrads when they synapse in prophase I.
-- The tetrads line up on the equator of the spindle in metaphase I.
-- The homologous chromsomes separate from each other and go to opposite poles in anaphase I, but they're still double-stranded.
-- So during telophase I, the forming nuclei are haploid. They have one of every kind of chromosome, but the chromosomes are still double-stranded, and that will never work in a gamete.

During meiosis II:
-- the double stranded chromosomes line up on the equator of the spindle
-- the two sister chromatids of these double-stranded chromosomes pull apart from each other during anaphase II
-- the new nuclei that form during telophase II have just one sister chromatid from each kind of chromosome.

Meiosis II starts with two cells that have one of each kind of chromosome -- in the form of double-stranded chromosomes.

Meiosis II ends with four cells that have one of each kind of chromosome --- in the form of sister chromatids that have pulled apart from the double-stranded form that they started with.

So one cell that is 2n --> 2 cells that are 1n but double-stranded --> 4 cells that are 1n but single-stranded.