TBR Reproduction Question

[soccatrini08]

I think there's a couple mistakes in the Bio Part 1 book. On page 214 of the latest edition it says in regards to ova production in females:

"The primary oocytes will eventually undergo the first meiotic division, caused by a surge in the gonadotropin LH...Once the first meiotic division is complete the secondary oocyte, which has 23 chromosomes, is formed. During this division one of the two daughter cells obtains all the cytoplasm while the other cell is just a small sphere of DNA called the first polar body. The secondary oocyte undergoes the second meiotic division only after fertilization has taken place. The product of that division is the ovum and a second polar body...The ovum now has 23 chromosomes. When sperm and ovum unite in fertilization, the complement of 46 chromosomes will be restored (23 from the male and 23 from the female)."

I have highlighted in bold what I think are mistakes or where my confusion lies. First off, why would the first meiotic divison give 23 chromosomes? Shouldn't it say 46 chromosomes since it's after the second meiotic division when the four daugher cells have 23 chromosomes each? Also, the passage says that after the second meiotic division the ovum now have 23 chromosomes, so clearly there has to be a mistake with the 23 chromosomes mentioned earlier. Please confim!

Secondly, if the second meiotic division is what gives rise to the ovum, and the ovum are what is fertilized during fertilization, how can the second meiotic division take place "only after fertilization takes place"? I'm confused!

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[indianjatt]

After the first meitotic division, there are indeed 23 chromosomes. This is because during metaphase, homologous chromosomes line up with each other. (So we have two chromosomes side by side). When we reach anaphase, the homologous chromosomes get separated (one chromosome goes to the one cell and the other homologous chromosome goes to the other). What's the result of one chromosome going to one cell and one to the other? Each cell ONLY has half the chromosomes. I think a picture will illustrate this better though.
http://en.wikipedia.org/wiki/Meiosis

The wiki link is a good one. See how they have 4 chromosomes drawn and after meiosis 1 there are only 2 chromosomes per cell?

 

[Hanguk]

I agree they did misuse the term "ovum" in that chapter to talk about an egg before and after fertilization, but I would assume ovum is what comes after fertilzation and primary oocyte before.

Also first meiosis division gives 23 chromosomes but 46 chromatids, the second meiosis division STILL gives 23 chromosomes but this time 23 chromatids in each cell. The number of chromatids changes but not the overall number of chromosomes. That's your confusion, I believe.