Define oogenesis. Briefly describe the stages of oogenesis in human females.

Dear Student,

Oogenesis is the process of producing the female gametes, the Ovum, from the primordial germ cells. 

Stages of oogenesis in human females are as below:
Stage 1
Primordial germ cell undergoes mitosis to produce two Oogonia. These cells are all Diploid. It occurs in fetal life.
Stage 2
Each Oogonia also undergoes mitosis to produce two diploid Primary Oocytes. It occurs in fetal life.
Stage 3
Each Primary Oocyte starts to undergo meiosis I replicating their DNA, but they are arrested at the first Meiotic Prophase. It occurs in fetal life.
Stage 4
The meiotic block is removed by the onset of puberty and the first Luteinising Hormone surge. The primary oocyte completes its first meiotic division producing a Secondary oocyte and the first polar body. The Secondary Oocyte enters Meiosis II and is arrested at metaphase II. The secondary oocyte is diploid.The oocyte enlarges due to a inrease (x50) in cytoplasmic volume. The oocyte is now 100-150µm. Ovulation occurs at this stage once the first meiotic division has been completed and secondary oocyte formed within the follicle
Stage 5
The secondary oocyte completes meiosis II producing the mature gamete, the Ova, which is haploid.This stage only ocurs after fertilisation of the secondary oocyte by the sperm has occurred.


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