Meiosis
Two divisions make four cells with half the chromosomes.
Making sperm and egg cells
Sperm and egg cells are made in reproductive organs. They are not made by plain mitosis.
If a parent cell divides twice in a row, how many cells can you get from it?
What this lesson covers
The idea
Meiosis occurs only in cells of reproductive organs and produces gametes: the parent cell divides twice to form four daughter cells, the first division halving the chromosome number and the second resembling mitosis.
Making sperm and egg cells
Sperm and egg cells are made in reproductive organs. They are not made by plain mitosis.
If a parent cell divides twice in a row, how many cells can you get from it?
- Four
- Two only
- Eight
Divide twice
Press + to step through. Then try 6 or 8 chromosomes.
Meiosis
Meiosis occurs only in the cells of reproductive organs and produces gametes. The parent cell divides twice, one after the other, to form four daughter cells. In the first division the number of chromosomes in each daughter cell is halved. The second division is similar to mitosis.
In animals, meiosis occurs in the testes (to make sperm) and the ovaries (to make eggs). In plants it occurs in the anthers (to form pollen grains) and the ovaries (to form egg cells).
- First division | Second division
- Cells after it | 2 | 4
- Chromosomes in each cell | half the parent’s | half the parent’s
- Similar to mitosis? | no, the number is halved | yes
Notes
Meiosis happens only in cells of reproductive organs and makes gametes: the parent cell divides twice to give four daughter cells. The first division halves the chromosome number; the second is similar to mitosis.
Check yourself
Where does meiosis occur in the human body?
A parent cell with 8 chromosomes undergoes meiosis. How many chromosomes does each of the four cells have?
Answer: 4 chromosomes
8 ÷ 2 = 4 chromosomes in each daughter cell.
How many times does the parent cell divide in meiosis?
Which division of meiosis halves the number of chromosomes?
- Only in cells of the reproductive organs — correct. Yes: testes and ovaries.
- In every body cell. Body cells divide by mitosis.
- Only in the skin. Skin cells divide by mitosis.
- Twice, one after the other — correct. Yes.
- Once. That is mitosis.
- Three times. It divides twice.
- The first division — correct. Yes.
- The second division. The second is similar to mitosis.
- Neither. The first division halves the number.