Spermatogenesis and oogenesis both use meiosis to make haploid gametes, but the results differ in number, size and timing. A good comparison answer gives both sides of each point.
This lesson opens the reproduction, development and growth chapter. If meiosis is unclear, see sequencing meiosis.
How do the two processes compare?
| Criterion | Spermatogenesis | Oogenesis |
|---|---|---|
| Where | Testes | Ovaries |
| Gametes from one germ cell | Four sperm | One ovum (plus polar bodies) |
| Size of gamete | Small | Large, with stored food |
| Movement | Motile, with a tail | Not motile |
| Timing | Continuous from puberty | Follows a monthly cycle from puberty |
| Chromosome number | Haploid (n) | Haploid (n) |
Worked example: a comparison question
Question: compare spermatogenesis and oogenesis. [4 marks]
A full answer:
- Spermatogenesis occurs in the testes, but oogenesis occurs in the ovaries.
- Spermatogenesis produces four sperm from one germ cell, but oogenesis produces one ovum from one germ cell.
- A sperm is small and has a tail for swimming, but an ovum is large, has stored food and cannot move by itself.
- Both processes involve meiosis and form haploid gametes.
The first three points pair the processes with “but”, and the fourth states a similarity. Questions that say “compare” reward at least one similarity or shared feature.
The mistake that costs marks
The common slip is to describe spermatogenesis and leave oogenesis as “the same but in females”. That sentence earns no mark, because the differences are the content.
| Wrong | Right | |
|---|---|---|
| Number | Both make four gametes | One germ cell makes four sperm but one ovum |
| Size | Gametes are the same size | The ovum is larger because it stores food |
| Chromosomes | Gametes are diploid | Both gametes are haploid |
A second slip is to say that sperm are made by mitosis. Mitosis keeps the chromosome number the same, while meiosis halves it, and gametes must be haploid so that fertilisation restores the diploid number.
Check yourself
Explain why the zygote is diploid even though both gametes are haploid.
Answer
The sperm and the ovum each carry one set of chromosomes (n). When they fuse at fertilisation, the two sets combine.
The zygote therefore has two sets (2n), which restores the diploid number. This is why gametes must be made by meiosis, which halves the chromosome number.
What to study next
The next lesson, explaining fertilisation and early development, follows the gametes after they meet. The biological data interpretation trainer provides more comparison tables.
Log one-sided comparisons in the mistake log and paper-error review. For a teacher to mark your comparison answers, see online one-to-one Biology tuition.