Asexual and sexual reproduction
The two strategies, and the advantages of each.
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 16.1.1Define asexual and sexual reproduction and discuss the advantages and disadvantages of each.
5 minute read
Asexual and sexual reproduction
Definitions
Asexual reproduction is the process resulting in genetically identical offspring from one parent. No gametes are involved, and the offspring are clones. Sexual reproduction is the process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote, producing genetically different offspring.
The trade-off
Everything about this topic follows from one fact: asexual reproduction produces no variation, sexual reproduction does. Asexual advantages — only one parent is needed, so no mate is required; it is fast; and all the good characteristics of the parent are kept exactly. Asexual disadvantage — no genetic variation, so if the environment changes or a new disease appears, the whole population is equally vulnerable. There is nothing for natural selection to work with. Sexual advantages — variation means some offspring may survive a change in conditions or resist a new disease, and variation is the raw material for natural selection and selective breeding. Sexual disadvantages — two parents are usually needed, it is slower, and useful parental combinations are broken up.
Where variation comes from
In sexual reproduction, gametes are made by meiosis, which halves the chromosome number and shuffles the genetic material. Fertilisation then combines two different sets at random, so no two offspring (other than identical twins) are alike.
Think of it like this
Asexual reproduction is photocopying; sexual reproduction is remixing. Photocopies are fast and faithful — but if the original has a flaw, every copy shares it, and none of them can adapt.
Worked examples
Method, step by step
A farmer grows a field of genetically identical potato plants produced asexually. Explain the risk of this.
- 1Asexual reproduction produces clones with no genetic variation.
- 2If a new disease appears that one plant is susceptible to, all the plants are equally susceptible.
- 3There is no resistant variation in the population, so the entire crop could be destroyed.
All the plants are genetically identical, so if a disease affects one it can affect all of them — with no variation, none will be resistant, risking total crop loss.
Common misconceptions
- Thinking variation in asexual offspring can arise "sometimes". Barring rare mutation, offspring are genetically identical clones.
- Believing sexual reproduction is simply "better". It is slower and needs a mate; in a stable environment asexual reproduction is often more efficient.
- Defining sexual reproduction as needing two parents rather than as the **fusion of gamete nuclei** — the fusion is the defining feature.
In the exam
- Learn both definitions word for word: "genetically identical offspring from one parent" and "fusion of the nuclei of two gametes to form a zygote".
- When asked for advantages, always tie variation to a consequence — surviving disease or environmental change — rather than just saying "there is variation".