oogenesis question

[oboestr]

I am trying to understand how a primary oocyte with 46 chromosomes undergoes meiosis twice and still has 23 chromosomes. Meiosis 1 suggests 23 chromosomes and Meiosis 2 suggests 23/2 (plus 23 from the fertilizing sperm cell).

 

I do see some sources indicating chromosomes forming tetrads in the primary oocyte. This doubling of information is apparently not considered to be 92 chromosomes, but still just 46 by some descriptions. The secondary oocyte after meiosis 1 completes is labeled haploid with 23 chromosomes, but some representations appear to be diploid. Then, meiosis 2 reduces the ovum to a haploid cell with 23 chromosomes.

 

 

???

 

[jimmydasaint]

This seems more like a homework question, but I won't get paranoid about that.

Take a look at the animation in the link and, if there is still confusion, tell us where the problem lies.

https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

[oboestr]

 

Take a look at the animation in the link and, if there is still confusion, tell us where the problem lies.

https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

That cleared things up a little. "Mitosis and Meiosis II are identical." That was one source of my confusion. Also, the short video explains that meiosis 1 produces cells with half the number of chromosomes as the original germline cell. They appear to have the same # of chromosomes but simply joined in pairs by a (centrosome ?). I guess the key mechanism for me to remember and understand is the interphase doubling of the chromosomes (strand doubling) before meiosis 1 accounts for the chromosome counts throughout the process.

[jimmydasaint]

Well done! I find that there seems to be confusion over the words: "chromatid" and "chromosome" and they tend to be used loosely. The way I see it, all cells have 23 pairs of chromatids before interphase and then the chromatids are doubled after DNA replication before meiosis.