I was watching an animation video about Meiosis and this is what the video shows (pics attached.) It shows that before synthesis, each chromosome exists as single chromatid and then after replication, it has a sister chromatid. I am confused because germ cells are diploid, so shouldn't the S phase look like this? It should start with 23 chromosomes (46 different DNA's) and then replicated to 46 chromosomes (92 different DNA) which then get assorted into 4 different cells?
In terms of chromosome number
During meiosis, the meiocyte is a diploid cell ( 46 chromosomes for human). So during the S-phase , the meiocyte would contain 46 chromosomes.
At the end of meiosis I, the divided meiocyte contains 23 chromosomes so it's called the reductional division
At the end of meiosis II each cell contains 23 chromosomes.
In terms of chromatid number and number of DNA molecules
Meiocyte in S phase contains 2 chromatid in each chromosome, so the number of DNA molecules is doubled (if you consider that each chromatid is composed of a pair of DNA strands like in Watson Crick Model, then each chromosome of S phase contains 4 strands... So 46×4 strands of DNA is present. Often each helix / duplex is considered one DNA molecule , so in that case you have 46×2 molecules. So you have to be careful with the terminology mentioned.
After meiosis I there are 23 chromosomes in each divided cell with 2 chromatids in each chromosome...So there are 23×2 DNA molecules.
After meiosis II there are 23 chromosomes with 1 chromatid...So they contain only 23 DNA molecules.
At the beginning, germ cells are diploid and as far as I know they are the cells that give rise to gametes which are haploid.
Here how it goes, the germ cell is containing 46 chromosomes and in S phase, these chromosomes replicate so that each chromosome will be made of 2 chromatids resulting in 92 chromatid.
In meiosis I, the germ cell divides and the 46 chromosomes divide as well giving two cells each containing 23 chromosomes and 46 chromatid.
The meiosis yet hasn’t finished. In meiosis II, each daughter cell containing 23 chromosomes will divide to two daughter cells. In this division, the chromatids in each chromosome will separate. In other words, the 46 chromatids in each cell will divide and each cell from the new daughter cells will be containing 23 chromatids. So now we have 4 haploid cells each one containing 23 CHROMATIDS ( a gamete ) all coming form one original diploid germ cell.
Those chromatids will then be referred to as chromosomes.