6.1.3 Advantages and disadvantages of sexual and asexual reproduction
Asexual reproduction
Asexual reproduction
Reproduction involving only one parent, with no fusion of gametes, producing genetically identical offspring (clones) by mitosis.
- Asexual reproduction needs only one parent, so a single organism can populate a habitat on its own.
- It is faster than sexual reproduction and more efficient with time and energy, because there is no need to find a mate.
- When conditions are favourable, it can produce many identical offspring very quickly.
- Every offspring is a genetically identical clone of the parent, so a successful set of genes is passed on unchanged.
- Its main disadvantage is that it produces no genetic variation in the offspring.
- Because the offspring are identical, a single disease or change in the environment can wipe out the whole population.
Aphids reproduce asexually in spring to build up large numbers on a plant very quickly.
A disease that kills one clone can kill them all, because they are genetically identical.
Sexual reproduction
Sexual reproduction
Reproduction involving two parents, in which male and female gametes fuse at fertilisation to produce genetically varied offspring.
- Sexual reproduction involves two parents, whose gametes fuse so that offspring inherit a mixture of genes from each.
- This produces genetic variation, so the offspring differ from their parents and from one another.
- If the environment changes, variation means some offspring are more likely to have features that help them survive.
- These survivors reproduce and pass on the helpful alleles, so the species can adapt over generations by natural selection.
- Humans make use of this variation in selective breeding, choosing and breeding organisms with useful features to increase food production.
- The disadvantages are that it is slower, needs two parents and usually a mate, and uses more time and energy.
The variation from sexual reproduction is the raw material that both natural selection and selective breeding act on.
Do not write that sexual reproduction is simply better; its variation is an advantage, but the time, energy and need for a mate are real costs.
Organisms that use both
- Many organisms can reproduce both ways and switch depending on their circumstances.
- When conditions are good they reproduce asexually to build up numbers quickly, and when conditions get harder they reproduce sexually to create varied offspring.
- The malarial parasite reproduces asexually inside the human host but sexually inside the mosquito.
- Many fungi reproduce asexually by spores but also reproduce sexually to give variation.
- Many plants produce seeds sexually but also reproduce asexually, such as strawberry plants spreading by runners and daffodils by bulb division.
A strawberry plant spreads by runners in summer and also makes flowers and seeds by sexual reproduction.
- Give two advantages of asexual reproduction.
- Why is a population of identical clones at risk from a new disease?
- How does the variation from sexual reproduction help a species survive a change in its environment?
- How does sexual reproduction make selective breeding possible?
- Name one organism that reproduces both sexually and asexually, and say where each method happens.
