S4.2.3 For the adult
Meiosis and sex cells
A baby has 46 chromosomes in its cells. But a sperm and an egg joined to make it. How is that possible if each parent has 46?
What this chapter teaches
Sex cells have half the chromosomes of body cells. Meiosis makes four different cells, and fertilisation brings the number back to 46. Random sorting and crossing over make every sex cell different. Mitosis makes two identical cells.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why would it be a problem if sperm and eggs had 46 chromosomes?
- What is the difference between mitosis and meiosis? What is one job of each?
- Why are brothers and sisters from the same parents not the same?
After the chapter, the learner can
- Explain why sex cells have half the chromosomes of body cells
- Compare mitosis and meiosis
What they copy into their notebook
Sex cells have 23 chromosomes, half of 46. Fertilisation makes 46 again. Meiosis: 4 different cells. Mitosis: 2 identical cells. Random sorting and crossing over make the difference.