Sexual and asexual reproduction (AQA GCSE Biology Combined Science): Revision Notes
Sexual and asexual reproduction
Living things can make new individuals in two main ways. Understanding these different types of reproduction is important for your GCSE exam.
What is sexual reproduction?
Sexual reproduction happens when male and female gametes combine together. This process creates offspring that are genetically different from their parents.
Gametes are special reproductive cells:
- Sperm cells and egg cells in animals
- Pollen cells and egg cells in flowering plants
How gametes are made
Gametes form when cells in reproductive organs divide by meiosis. This is a special type of cell division that works like this:
- The parent cell is diploid - it has two sets of chromosomes
- During meiosis, the cell divides twice
- This creates four daughter cells
- Each daughter cell is haploid - it has only one set of chromosomes
- These haploid cells become gametes
Worked Example: Human Chromosome Numbers
Human body cells have 46 chromosomes (diploid). During meiosis, this number is halved. Therefore, human gametes have 23 chromosomes (haploid).
Fertilisation
Fertilisation happens when a sperm cell and egg cell join together. The result is called a zygote.
The zygote has:
- Two sets of chromosomes again (diploid)
- Mixed genetic information from both parents
- The ability to divide by mitosis to form an embryo
This mixing of genetic information creates variation in the offspring.
What is asexual reproduction?
Asexual reproduction involves only one parent. No gametes combine together, so there is no mixing of genetic information.
Key features of asexual reproduction
- One parent only
- No fusion of gametes
- No mixing of genetic information
- Offspring are clones - they are genetically identical to the parent
- Cell division happens by mitosis (not meiosis)
The key difference is that asexual reproduction produces identical offspring (clones) while sexual reproduction creates genetic variation.
Examples of asexual reproduction
Bacteria reproduce asexually. They simply divide to create identical copies of themselves.
Other examples include budding in yeast, runners in strawberry plants, and fragmentation in some worms.
Comparing sexual and asexual reproduction
| Sexual reproduction | Asexual reproduction |
|---|---|
| Two parents needed | One parent only |
| Gametes fuse together | No gamete fusion |
| Genetic information mixes | No mixing of genetic information |
| Creates variation | Creates identical clones |
| Uses meiosis to make gametes | Uses mitosis only |
Key Points to Remember:
- Sexual reproduction needs two parents and creates genetically different offspring through fertilisation
- Asexual reproduction needs only one parent and creates identical clones
- Meiosis makes haploid gametes from diploid cells
- Fertilisation combines gametes to restore the diploid number
- Sexual reproduction creates variation, asexual reproduction creates clones