What is the difference between sexual and asexual reproduction, and what is meiosis?
Sexual and asexual reproduction, the formation of gametes by meiosis, the advantages and disadvantages of each type of reproduction, and the role of fertilisation in producing variation.
A focused answer to AQA GCSE Biology 4.6.1.1, covering sexual and asexual reproduction, the formation of gametes by meiosis, and the advantages and disadvantages of each type of reproduction.
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What this dot point is asking
AQA wants you to compare sexual and asexual reproduction, explain how meiosis forms gametes, and weigh up the advantages and disadvantages of each type of reproduction.
Sexual reproduction
In humans the gametes carry 23 chromosomes each (half the normal number); when they fuse at fertilisation the full number of 46 is restored. The combination of which gametes fuse is random, which is one source of the variation in sexually produced offspring.
Meiosis
This is different from mitosis, which produces two genetically identical cells for growth and repair. The halving of chromosomes in meiosis is essential, because if gametes had the full number, the chromosome number would double every generation.
Asexual reproduction
Advantages and disadvantages
- Sexual reproduction: produces variation, which helps a species survive environmental change and is the raw material for natural selection and selective breeding; but it needs two parents (and so the time and energy to find a mate) and is slower.
- Asexual reproduction: is fast, needs only one parent, and lets an organism reproduce quickly and successfully in good, stable conditions; but it produces no variation, so the whole population is vulnerable to the same disease or environmental change.
Some organisms can do both, switching strategy to suit conditions. Many plants, such as strawberries, reproduce asexually by runners when conditions are good (spreading quickly to colonise an area) and sexually by seeds to create variation. Malarial parasites reproduce asexually in the human host but sexually in the mosquito, and many fungi reproduce asexually by spores when conditions are favourable but sexually to produce variation when they are not. This flexibility gives the best of both: rapid increase in numbers when conditions are good, and variation that may help survival when conditions change. AQA likes to give an unfamiliar organism and ask you to suggest why being able to use both types of reproduction is an advantage, so applying the variation-versus-speed idea is the key skill.
Try this
Q1. State one advantage of sexual reproduction. [1 mark]
- Cue. It produces genetic variation, helping a population survive change.
Q2. How many genetically different cells does meiosis produce from one cell? [1 mark]
- Cue. Four.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20184 marksCompare sexual and asexual reproduction. In your answer refer to the number of parents, the role of gametes and meiosis, and the variation in the offspring.Show worked answer →
A 4-mark compare question rewards linked comparative points.
Sexual reproduction involves two parents and the fusion of gametes (sex cells) at fertilisation, whereas asexual reproduction involves only one parent and no gametes. In sexual reproduction the gametes are made by meiosis, which halves the chromosome number, whereas asexual reproduction uses mitosis. As a result, sexual reproduction produces offspring with genetic variation, whereas asexual reproduction produces genetically identical clones.
Markers reward at least three comparisons (number of parents, gametes and meiosis versus mitosis, and variation versus clones) using comparative language.
AQA 20214 marksSome organisms can reproduce both sexually and asexually. Suggest and explain the advantages to such an organism of being able to use both types of reproduction in different conditions.Show worked answer →
A 4-mark suggest-and-explain question rewards reasoning for each type.
In good, stable conditions the organism can reproduce asexually, which is fast, needs only one parent, and produces many genetically identical offspring quickly, so it can colonise the area rapidly.
If conditions change or become unfavourable, sexual reproduction is an advantage because it produces genetic variation, so some offspring may have characteristics that let them survive the new conditions or a new disease, and the species is more likely to survive.
Markers reward asexual being fast and not needing a mate in good conditions, and sexual producing variation that aids survival when conditions change.
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Sources & how we know this
- AQA GCSE Biology (8461) specification — AQA (2016)