4.6.1.3 - Advantages and Disadvantages of Sexual and Asexual Reproduction

The comparison frame

Sexual reproduction and asexual reproduction were introduced in the previous specification point. This lesson uses those definitions only as a starting point, then asks why an organism might benefit from one method rather than the other.

The important result of sexual reproduction is variation. Variation means differences in the characteristics of individuals in a population. In this topic, variation matters because different offspring may have different chances of surviving if the environment changes.

The important result of asexual reproduction is speed and efficiency. If the parent organism is already well suited to the conditions, many identical offspring can be produced quickly.

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Use this trade-off throughout the lesson:

Sexual reproduction: advantages and costs

The main advantage of sexual reproduction is that it produces variation in the offspring. This does not mean every offspring will survive. It means there are differences for natural selection to act on.

If the environment changes, variation can give a survival advantage. For example, if a new disease, predator or environmental condition affects a population, some offspring may have characteristics that make them more likely to survive than others. Those survivors are more likely to reproduce and pass on the helpful characteristics.

This is why sexual reproduction is useful in changing conditions: it spreads risk. The offspring are not all genetically identical, so one harmful change is less likely to affect every offspring in exactly the same way.

Humans can speed up natural selection in selective breeding. In selective breeding, humans choose organisms with useful characteristics and breed from them. Because sexual reproduction produces variation, there can be individuals with characteristics humans want, such as higher yield, larger fruit, more milk, or faster growth. Selecting and breeding those individuals can increase food production.

The cost is that sexual reproduction usually needs a mate or two parents. Finding a mate, producing gametes, courtship or pollination can take time and energy. Sexual reproduction is often slower than asexual reproduction, so it may produce fewer offspring in the same time.

Asexual reproduction: advantages and costs

Asexual reproduction has four linked advantages in the AQA specification:

This method is especially useful when conditions are favourable. Favourable conditions mean the current environment suits the organism: enough resources, suitable temperature or moisture, and no major new pressure that makes the parent's characteristics a problem.

The disadvantage is the same feature seen from the other side. Asexual reproduction produces genetically identical offspring. If conditions change, the offspring may all have the same weakness because there is little variation for natural selection to act on.

For example, if a population of identical organisms is affected by a new disease, many individuals may be equally vulnerable. A population with more variation has a better chance that some individuals will have characteristics that help them survive.

Organisms using both methods

Some organisms reproduce by both sexual and asexual methods depending on the circumstances. AQA restricts your required knowledge to the organisms named in this section.