Mitotic division producing genetically identical diploid cells

One cell becomes two

Tap each stage to follow one chromosome through it.

1. 1Start: one cell, its chromosomes in the nucleusInside the nucleus are chromosomes: tightly coiled strands of DNA that carry the cell's genetic material. A human body cell has 46 of them.+
2. 2Interphase: copy everythingBefore mitosis starts, the DNA is replicated. Each chromosome is now made of two identical chromatids, still joined together, so it still counts as one chromosome. A human body cell still has 46. The sub-cellular structures are copied too.+
3. 3Mitosis: split and pull apartEach chromosome splits into two identical chromatids, and they are pulled to opposite ends of the cell.+
4. 4Cytokinesis: divide the cellThe cell membrane and the cytoplasm divide, so the two ends become two separate cells.+
5. 5Result: two matching cellsTwo genetically identical diploid cells, each with the full set of chromosomes.+

Predict, then check

Now scale it up: not one division, but lots of them in a row.

After fertilisation, a human zygote has 46 chromosomes. It divides by mitosis, then the new cells divide by mitosis, and they keep going until there is an embryo. What will a cell in that embryo contain?

What you need to know

• Chromosomes are tightly coiled strands of DNA, found in the nucleus, that carry the genetic material.
• Diploid means the full number of chromosomes, with two copies of each — 46 (23 pairs) in human body cells. Haploid means half the number, one copy of each — 23 in human gametes.
• Mitosis happens in order: DNA replicated in interphase, then identical chromatids pulled to opposite ends, then cytokinesis.
• Mitosis makes 2 genetically identical diploid cells; meiosis makes 4 genetically different haploid cells.

The big picture

Mitosis is cell division that turns one cell into two genetically identical diploid cells. First, in interphase, the DNA is replicated. Then each chromosome splits into two identical chromatids that are pulled to opposite ends. Finally cytokinesis divides the membrane and cytoplasm. Meiosis is different: it makes four genetically different haploid cells.

⚠ Watch out

Saying that mitosis halves the chromosome number, so a human body cell with 46 chromosomes makes cells with 23. That halving belongs to meiosis. In mitosis the DNA is replicated before the cell divides, so each new cell keeps all 46.

Memory hook

Copy, then share. Mi-TWO-sis gives TWO cells that match: copy every chromosome first, share the copies out exactly, mix nothing.

Check yourself

Without looking back: name the three things that happen, in order, when a body cell divides by mitosis. What do the two new cells share with the original?