What is Oogenesis?
Oogenesis is the process by which the female gametes (also called ova or eggs) are formed in the ovaries. It is a type of gametogenesis (the general term for forming sex cells), and it only happens in females.
1. Starts Before Birth
• In the ovaries of a female fetus, diploid cells called oogonia begin dividing.
• These cells enter meiosis (a special kind of cell division) and become primary oocytes.
• These oocytes pause in the first stage of meiosis (prophase I) and stay like that until puberty.
2. Resumes at Puberty
• Every month during the menstrual cycle, one primary oocyte continues meiosis.
• It divides into:
• One large secondary oocyte (which can become the egg)
• One small polar body (which dies)
3. Ovulation
The secondary oocyte is released from the ovary.
If sperm fertilizes it, it finishes meiosis and becomes a mature ovum (egg).
If it’s not fertilized, it is shed during menstruation.
4. Unequal Division
• During each step, the cell divides unevenly.
• Only one functional egg is made, and the other cells (polar bodies) die.
• This ensures the egg has lots of nutrients for the embryo.
What is it for?
1. Producing Eggs
• It creates mature egg cells that can be fertilized by sperm.
• Only one egg is usually released each month during the menstrual cycle.
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2. Enabling Fertilization
• The egg made in oogenesis carries half the genetic material (23 chromosomes in
humans).
• When it joins with a sperm (which also has 23 chromosomes), they form a zygote with 46 chromosomes — The start of a new human being.
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3. Supporting Early Development
• The egg has nutrients and structures needed to support the very early stages of embryo development Before implantation in the uterus.
Favourite Part/ note/ summary—Oogenesis is the process where eggs are made in females. It starts before birth, stops for a while, and starts again during puberty. Each month, one egg is made that can be fertilized by sperm. If that happens, it can grow into a baby. If not, it’s removed during the period.
At what stage in a female’s life does oogenesis begin, and when does it complete?
What are the main stages of oogenesis, and what key changes occur during each?
Why does oogenesis produce only one viable ovum from each primary oocyte, unlike spermatogenesis?
How do hormonal changes regulate the process of oogenesis?
What is the significance of the polar bodies formed during oogenesis?
Keywords :
Mitosis
Meiosis