Reproduction: Question 6
Syllabus 16.1, 16.2
A gardener grows strawberry plants in two ways. Some new plants grow asexually from runners: long stems that creep along the ground and take root, forming new plants that are genetically identical to the parent plant. Other new strawberry plants grow sexually from seeds, which form after strawberry flowers are pollinated and fertilised.
(a) State two advantages to the gardener of producing new plants asexually, using runners, rather than from seed. [2]
(b) State two advantages of producing new plants sexually, from seed, rather than by runners. [2]
(c) A new fungal disease is introduced into the field. Explain why a population of strawberry plants produced only by runners could be more severely affected by this disease than a population produced from seed. [2]
Show worked solution Hide worked solution
Worked solution
Part (a): Advantages of asexual reproduction (runners)
Producing new strawberry plants from runners does not depend on pollination taking place, so the gardener can rely on new plants forming even in the absence of pollinators. Because no gametes fuse, every new plant is genetically identical to the parent plant, which guarantees that a parent with desirable characteristics (for example, good-tasting or high-yielding fruit) will pass those characteristics on unchanged.
Part (b): Advantages of sexual reproduction (from seed)
Producing new plants from seed involves the fusion of gametes from (potentially) two genetically different parent plants, so the offspring show genetic variation. This variation increases the chance that at least some offspring will be well suited if growing conditions change, for example if the climate becomes drier or a new pest arrives. Seeds are also easily dispersed away from the parent plant, allowing the species to spread into and colonise new areas.
Part (c): Why an asexual population is more vulnerable to disease
All the plants produced by runners are genetically identical to one another, since no gamete fusion has introduced any variation. If the fungal disease is able to infect and kill one of these plants, it can infect and kill every other plant in the population in exactly the same way, because none of them differs genetically in its ability to resist the fungus. This could destroy the entire runner-produced population.
A population grown from seed, in contrast, contains genetic variation between individuals. It is more likely that at least some of these plants carry alleles that give them some resistance to the fungus, allowing them to survive and reproduce even if many other plants in the population are killed.
Final answers
- (a) No pollinator needed; offspring genetically identical, guaranteeing the parent’s desirable characteristics.
- (b) Genetically varied offspring, better able to cope with a changing environment; seeds allow dispersal to new areas.
- (c) Runner-produced plants are all genetically identical, so a disease that can infect one can infect all of them; a seed-grown population has genetic variation, so some individuals may resist the disease and survive.