Asexual Reproduction and Mitosis — Study Notes

A spider plant grows tiny baby plants dangling off long runners — no flowers, no seeds, no second parent involved. Snip one off, pot it, and it grows into a full spider plant that's a genetic carbon copy of the one it came from. That copying trick has a name, and a single cell-level process makes it possible.

The Core Idea: Copy First, Then Split

Asexual reproduction means new offspring come from a single parent, with no mixing of two parents' genetic material — so the offspring end up genetically identical to that parent. Bacteria, yeast and many plants reproduce this way.

What makes it possible at the cellular level is mitosis: a dividing cell first duplicates every bit of its genetic material, then splits into two daughter cells, each receiving one full, matching set. Because nothing is left out and nothing is shared between two different sources, the daughter cells are exact genetic matches of the original — and, crucially, the chromosome number stays the same from parent cell to daughter cell. Mitosis isn't only for reproducing whole organisms, though — the same duplicate-then-divide process also drives ordinary growth and wound repair inside a single body, which is why examiners test it across more than one context.

Worked Example — Tracking Chromosome Number Through Mitosis

1. An onion root-tip cell contains 16 chromosomes before it divides.
2. During mitosis, this cell duplicates its chromosomes first, so a complete second set exists inside the one cell — 32 in total, but still inside a single nucleus at this stage.
3. The cell then splits into two daughter cells, and the duplicated sets are shared out evenly, one full set per daughter.
4. Result: each daughter cell ends up with 16 chromosomes — matching the original parent cell exactly, because doubling happens only briefly before the split restores the starting number.

Notice the number never overshoots permanently: doubling and splitting cancel out, which is exactly why mitosis is described as maintaining chromosome number rather than increasing it.

The full lesson below works through the remaining scenarios — growth, repair and genetic variation — plus a listen-along audio walkthrough and a practice worksheet.