genetics doubt. -

[ArchivalUser]

BR

Guys could someone please clear this concept regarding meiosis 1?

1.if a spermatogonia/oogonia originally is at 46 2n (2 copies of same gene on 1 chromososme).then at the end
of meiosis (reduction division)we have 23 1n in each gamete before they go in for fertilization to make it 46 2n.
I understand this very well.

what I dont understand is the 46 4n in the beginning of meiosis 1.just because homologous chromosomes allign at
the metaphase plate (in the same cell) how does 46 2n become 46 4n.? is it due to DNA replication.?

your input would be of great help.
thank you.

[ArchivalUser]

cue

You are correct BR,
It's due to DNA replication. The S phase of DNA cycle.
M1 is followed after this, in which you will end up with 23 2n, because of the cell division, and then finally m2 will leave it at 23 1n.
By the way, the chromosome numbers, and whether haploid or diploid of each steps are high yield in the exam.

[ArchivalUser]

BR

thanks cue.