Asexual Reproduction and Its Comparison With Sexual Reproduction
Asexual reproduction is production of genetically identical offspring (clones) from a single parent by mitosis, with no fusion of gametes. This IGCSE topic goes beyond the GCSE spec by requiring named examples of natural asexual reproduction in plants (runners in strawberry plants, bulbs in daffodils/onions, tubers in potatoes) and a systematic comparison of asexual and sexual reproduction across genetic variation, speed, energy cost and reliance on a mate or pollinator, so that students can argue which method suits a given situation (for example, a farmer growing a crop with a desirable trait, or a species colonising a new habitat).
Method
- Define asexual reproduction precisely: one parent produces offspring by mitosis, so the offspring (clones) are genetically identical to the parent and to each other, with no fusion of gametes and no genetic variation from the process itself.
- Learn at least one named natural example and describe its mechanism: a strawberry plant sends out a runner (a horizontal stem) that grows a new, genetically identical plant at a node where it touches the soil; a daffodil bulb stores food and produces new bulbs (offsets) that grow into separate plants; a potato tuber is a swollen underground stem that grows new shoots (each capable of becoming a new plant) from its buds ('eyes').
- Build a structured comparison table in your head with these four headings: genetic variation (asexual: none, all offspring identical; sexual: high, offspring vary due to the mixing of two parents' alleles), speed and energy cost (asexual: fast, only one parent needed, no need to find a mate; sexual: slower, requires two parents or a pollinator), reliability in a stable environment (asexual: reliably reproduces a successful genotype; sexual: risk of producing less well-adapted offspring), and response to a changing environment or disease (asexual: no variation, so a whole clonal population can be wiped out by the same disease or environmental change; sexual: variation gives some offspring a chance of surviving).
- For 'explain why a farmer/gardener would choose asexual reproduction' questions, argue from the genetic-identical point: cloning guarantees every offspring has the exact same desirable characteristics (for example, fruit yield or flavour) as the parent, which sexual reproduction cannot guarantee because of variation.
- For 'explain why sexual reproduction is an advantage' questions, argue from the variation point: variation means some offspring have combinations of alleles that make them better suited to a new or changing environment, or resistant to a disease that affects other members of the population, so the species/population is less likely to be wiped out.
- When a question gives artificial cloning methods (for example, taking plant cuttings or tissue culture), classify them as asexual reproduction too and apply the same genetically-identical reasoning, since no gametes are involved.
Worked example
A commercial strawberry grower wants every plant in a new field to produce large, sweet fruit identical to a prize-winning parent plant. Explain why the grower should propagate new plants using runners rather than growing new plants from seed.
- Identify the type of reproduction each method uses: runners are asexual reproduction (mitosis, one parent); growing from seed is sexual reproduction (fusion of gametes, two parents, or self-pollination with recombination).
- State what asexual reproduction guarantees: offspring produced from runners are genetically identical clones of the parent plant.
- Link this to the grower's goal: because the offspring are genetically identical, every new plant is certain to have the same genes for large, sweet fruit as the prize-winning parent.
- Explain why seed would not guarantee this: seeds are produced by sexual reproduction, so the offspring's alleles are a new combination from two parents (or from recombination), meaning some seedlings might not produce fruit as large or sweet as the parent.
- Final answer: the grower should use runners, because asexual reproduction produces genetically identical offspring, guaranteeing every new plant has the parent's desirable large, sweet fruit alleles, whereas seed-grown plants would show variation and might not match the parent.
Practice questions
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Q1Define asexual reproduction.Show answer
Answer: Reproduction from a single parent, by mitosis, producing offspring that are genetically identical to the parent, with no fusion of gametes.
Q2Name one type of plant structure used in natural asexual reproduction, and name a plant that uses it.Show answer
Answer: Any one of: a runner (strawberry), a bulb (daffodil or onion), a tuber (potato).
Q3State the type of cell division that produces genetically identical offspring in asexual reproduction.Show answer
Answer: Mitosis.
Q4State one disadvantage of asexual reproduction for a population facing a new plant disease.Show answer
Answer: All the offspring are genetically identical, so if the disease can infect one plant it is likely to be able to infect all of them, and the whole population could be wiped out (no variation to give any resistance).
Q5A gardener grows 40 potato plants from tubers taken from one parent plant. Explain why all 40 plants are expected to have identical leaf colour to the parent.Show answer
Answer: The tubers were produced by asexual reproduction (mitosis) from a single parent, so all the new plants are clones and are genetically identical to the parent, including for the gene(s) controlling leaf colour.
Q6State one advantage of sexual reproduction over asexual reproduction in a changing environment.Show answer
Answer: Sexual reproduction produces genetically varied offspring, so some offspring may have a combination of alleles suited to the new conditions and are more likely to survive and reproduce, whereas asexual offspring are all identical and equally vulnerable.
Exam-style questions
Written in the style of a IGCSE Science exam paper, with a full mark scheme.
State two ways in which asexual reproduction differs from sexual reproduction in terms of the number of parents involved and the genetic variation produced.
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A farmer grows a field of a crop entirely by planting tubers from a single high-yielding parent plant. A blight (a fungal disease) then spreads through the region. In one field grown from tubers, 95% of plants were destroyed by the blight. In a neighbouring field of the same crop grown from seed (from cross-pollinated plants), only 40% of plants were destroyed. Explain this difference.
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A plant breeder is deciding whether to propagate a newly developed variety of apple tree, which has an unusually sweet fruit caused by a rare combination of alleles, using grafted cuttings (asexual reproduction) or by growing new trees from its seeds (sexual reproduction). Evaluate which method the breeder should choose, considering genetic reliability, speed, and the risk from disease.
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Free printable worksheet
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