Question about meiosis & oogenesis

Question

Hello, I am confused about oogenesis. As far as I can gather, oogenesis is meiosis for the female sex cells. I understand that the secondary oocyte stalls at metaphase 2 and is then ovulated. If it is penetrated by sperm it will complete meiosis 2. I am reading about meiosis in my textbook and it is saying that in prophase of meiosis 1, the replicated chromosomes seek out their homoilogous partners to pair up with them (synapsis) and that crossover occurs here, exchanging maternal and paternal genetic material. So where is this happening? I though the oocyte already passed meiosis 1 in the ovary so how is it mixing with maternal genetics at this stage?

Answer 1

You are correct in that oogenesis is just female meiosis. I think your book was just backtracking and saying that during oogenesis at the point of Prophase I crossing over occurs. During oogenesis at Prophase I the homologous chromosomes inside the primary oocyte line up with each other and crossing over occurs between the maternal genetic information found in all cells and the paternal copy of the person's genetic information. Was that helpful or am I not understanding the question?

Answer 2

Hi Charolette,

 

Meiosis is a cell division that divides one parental cell into four daughter cells, each daughter cell contains half the number of chromosomes than parent cell. 

 

Oogenesis is the process of development of female gamete or egg from female germ cells. It  leads to formation of mature egg  from primary and secondary oocytes. 

 

During meiosis each parent cell first divides in two cells leading to first meiotic division where prophase is prolonged and has five distinct stages such as leptotene, pachytene, zygotene etc.

 

Second meiotic division divides two daughter cells of first meiotic division into 2 other daughter cells creating 4 daughter cells  in total from one parent cell. Here chromosomes are divided in number. For example, every cell in human body has 46 chromosomes but human egg and sperm have only 23 chromosomes each. Hope you get the point.

 

When sperm penetrates egg at the onset of fertilization, the fusion of egg and sperm causes fertilization and a new cell called zygote that  has 46 chromosomes, 23 chromosomes from each parent.  

 

Homologous chromosomes pair in zygotes, crossing over and recombination causes exchange of genetic material thereby causing unique combination of genes and phenotype. That is why siblings from same parents look different and have different personalities.

 

Meiosis only occurs in germ cells, all other cells divide by mitosis.

 

Hope this is clear and  helpful.

 

Best,