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Module 03

Making eggs and sperm

How the body makes eggs and sperm: meiosis in plain words, the long life of a follicle, the sperm production line, the hormones behind both, and what age changes.

  • 5lessons
  • 23 minreading
  • 6quiz questions
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The lessons and the quiz in this module are part of the Fertility with Kara Package. Module 1 is free to read.

Your way through Module 03

  1. Lesson 3.1 · 4 min Meiosis, explained simply How eggs and sperm end up with exactly half a set of chromosomes, and why no two of them are alike.
  2. Lesson 3.2 · 4 min Where eggs and sperm begin How the cells that become eggs and sperm are set aside in the first weeks of life, and why a woman's eggs are as old as she is.
  3. Lesson 3.3 · 5 min From follicle to egg How a resting follicle wakes up, grows for months, and releases one egg, and which hormones run the process.
  4. Lesson 3.4 · 5 min Making sperm How the testes turn stem cells into sperm in about two to three months, and the hormones that keep the production line running.
  5. Lesson 3.5 · 5 min How age affects eggs and sperm Why a woman's age matters so much for her eggs, why a man's age matters less but still a little, and what egg quality means.
  6. Quiz6 questions · 5 to passNot taken BadgeModule 03Earned with the quiz

Learning aims

By the end of this module you will be able to:

  • Explain how meiosis halves the number of chromosomes and makes every egg and sperm genetically unique.
  • Describe where eggs and sperm come from, and why a woman's eggs are formed before she is born.
  • Describe the stages of follicle growth and what the LH surge does to the egg.
  • Describe how sperm are made in the testes, how long it takes, and which hormones control it.
  • Compare how age affects eggs and sperm, and explain the difference between egg quantity and egg quality.

The module in brief

The module in brief
  • Meiosis uses two divisions to give each egg and sperm 23 chromosomes, one from each pair, newly mixed by crossing over.
  • Eggs and sperm both come from primordial germ cells set aside in the first weeks after fertilisation.
  • A woman's eggs are formed before birth and wait, paused in meiosis, inside resting follicles whose number falls steadily with age.
  • A follicle grows for months; in each cycle usually one becomes dominant, and the LH surge restarts meiosis and triggers ovulation.
  • Sperm are made continuously from stem cells in the testes, a process of about two to three months controlled by FSH, LH and testosterone made inside the testes.
  • Testosterone taken from outside the body switches off sperm production.
  • With age, eggs become fewer and more often carry the wrong number of chromosomes; sperm change more gradually.
A note from Kara

Thank you for choosing to learn with me

I know you had many places to look for answers, and you chose this course. Thank you. It means a lot to me that you trust me with something this close to your heart.

Every lesson here is something I wish every couple could hear before they sit down with their clinic: how a life begins, what happens in the lab, and what the words on your report mean. Take it slowly. Short lessons, one at a time, are the way the science sinks in.

If a lesson raises a question about your own body or your own embryos, write it down and take it to your healthcare professional. That is exactly what this course is for.

Warmly, Kara

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