Asexual Reproduction

Definition. Asexual reproduction produces GENETICALLY IDENTICAL offspring from ONE parent. There's NO fusion of gametes.

Examples.

1. Binary fission (bacteria, some protoctists).

• Single cell DNA replicates.
• Cell pinches in the middle.
• Splits into two daughter cells, each identical to the parent.
• Bacteria can do this every ~20 minutes in good conditions.

2. Budding (yeast, Hydra).

• A small bud grows on the parent.
• Detaches as a new individual.

3. Runners (strawberries, spider plants).

• Horizontal stems grow along the ground.
• New plant grows where the stem touches soil.
• Identical to parent.

4. Tubers (potatoes, dahlias).

• Swollen underground stems.
• Each 'eye' on a potato can grow into a new plant.

5. Spores (fungi, mosses, ferns).

• Tiny reproductive cells released into the environment.
• Each can grow into a new individual.

Worked qualitative. Why can a single bacterium become billions in 24 hours?

• Binary fission every 20 mins (in good conditions).
• 1 → 2 → 4 → 8 → ... 2³⁰ in ~10 hours.
• Bacterial colonies can grow visibly overnight.
• Why food spoils so quickly without refrigeration.

Cambridge tip. Always state 'genetically identical offspring' AND 'one parent'. Both phrases are key.

Advantages:

• Fast — no time wasted finding a mate, producing gametes, fertilising.
• One individual can populate an area on its own.
• Reliable in STABLE conditions — if the parent is well-adapted, identical offspring will be too.
• Energy-efficient — no large investment in flowers, courtship, parental care.

Disadvantages:

• No genetic variation — offspring identical to parent.
• Whole population is vulnerable to environmental change — if conditions shift, all individuals respond the same.
• Disease can wipe everyone out — if one is susceptible, all are.
• Slower evolution — without variation, natural selection has nothing to work on; populations adapt slowly.

Famous example: Irish potato famine (1845-1852).

• Most Irish potatoes were one variety, all clones.
• A potato blight (fungus) struck.
• Every plant was equally susceptible → entire crop failed.
• ~1 million Irish died of starvation; another million emigrated.
• A lesson in the danger of monoculture and lack of variation.

Worked qualitative. Why do farmers SOMETIMES choose to grow asexually-reproduced crops?

• Predictable yield (offspring identical to a known good parent).
• Easier to manage uniform crops.
• Reduces risk of poor offspring.
• BUT — needs constant introduction of new varieties to avoid blights wiping everything out.

Cambridge tip. When asked for advantages/disadvantages, give 2 of each WITH reasons. Cambridge marks each.