Differences between Sexual & Asexual Reproduction

Every species must reproduce — make new individuals (called offspring) — or it would die out. There are two types of reproduction in living things, and the exam wants you to compare them:

• Sexual reproduction — involves two parents and the joining (fusion) of two special sex cells called gametes.
• Asexual reproduction — involves only one parent and no gametes at all.

The big idea to hold in your head is what each one does to the offspring's genes:

• Sexual reproduction mixes genes from two parents, so the offspring show variation — they are all slightly different from each other and from their parents.
• Asexual reproduction copies one parent, so the offspring are genetically identical to the parent and to each other. We call genetically identical offspring clones.

Examples you can picture:

• Sexual: humans, most animals, and flowering plants (pollen + egg cell).
• Asexual: bacteria splitting in two, a strawberry plant sending out runners, a spider plant making baby plantlets, and a potato growing from tubers.

Exam tip. The whole subtopic comes down to a small set of contrasts: parents (two vs one), gametes (yes vs no), variation (varied vs identical clones) and cell division (meiosis vs mitosis). Learn these four pairs and you can answer almost any question on spec 3.1.

In sexual reproduction there are two parents. Each parent makes special sex cells called gametes:

• In animals, the gametes are the sperm (male) and the egg cell / ovum (female).
• In flowering plants, the gametes are in the pollen (male) and the egg cell / ovule (female).

A gamete has only half the normal number of chromosomes, because it is made by a special type of cell division called meiosis. Meiosis also shuffles the genes, so every gamete is slightly different.

At fertilisation, a male gamete fuses (joins) with a female gamete to form a single cell called a zygote. The zygote now has the full set of chromosomes again — half from each parent — and it grows into the new offspring.

Because the offspring gets a mixture of genes from two different parents, sexual reproduction produces genetic variation: the offspring are all different from one another and from their parents (think how brothers and sisters are not identical).

Here is the key sequence:

Exam tip. The marking points for sexual reproduction are: two parents, gametes fuse / fertilisation, meiosis, and genetic variation. Use the precise words gametes, fertilisation and variation.

In asexual reproduction there is only one parent. There are no gametes and no fusion — instead, the parent simply copies itself.

The cell division involved is mitosis. Mitosis makes an exact copy of the parent's chromosomes, so the offspring receive exactly the same genes as the parent.

This means the offspring are genetically identical to the parent and to each other. Genetically identical individuals are called clones.

Common examples of asexual reproduction:

• Bacteria split in two (binary fission).
• A strawberry plant grows runners that root and form new plants.
• A spider plant produces small plantlets on the end of stems.
• A potato grows new plants from its tubers.

Because only one parent is needed, asexual reproduction is quick and there is no need to find a mate — very useful when a single organism arrives in a new, empty habitat. The catch is that every clone is identical, so they all have the same strengths and the same weaknesses.

Exam tip. The marking points for asexual reproduction are: one parent, no gametes / no fusion, mitosis, and genetically identical offspring / clones. The word clone is worth a mark — use it.

Each type of reproduction has clear advantages and disadvantages. The key driver is variation.

Sexual reproduction

• Advantage: produces genetic variation. If the environment changes (new disease, new climate, new predator), some of the varied offspring are likely to have features that help them survive — this also helps a species evolve and adapt.
• Disadvantage: needs two parents (so you must find a mate), takes more time and energy, and usually produces fewer offspring.

Asexual reproduction

• Advantage: needs only one parent (no mate required), is fast, and can produce many offspring quickly when conditions are good. Useful for rapidly colonising a favourable habitat.
• Disadvantage: offspring are identical clones with no variation. If the environment changes or a disease strikes, all of them are equally vulnerable, so the whole population could be wiped out.

A neat way to remember it: sexual reproduction "spreads the bets" with variation; asexual reproduction "copies a winner" quickly but puts all its eggs in one basket.

Exam tip. When asked for an advantage of sexual reproduction, the safe answer is variation → better chance of survival if the environment changes. For asexual, the safe answers are fast / only one parent needed / no mate needed.

This is the single most important thing to memorise for spec 3.1. Examiners frequently ask you to complete a table of differences, so learn it row by row.

Feature	Sexual reproduction	Asexual reproduction
Number of parents	Two parents	One parent
Gametes (sex cells)	Yes — two gametes fuse at fertilisation	No gametes, no fusion
Type of cell division	Meiosis (to make the gametes)	Mitosis
Genetics of offspring	Genetically different — variation	Genetically identical — clones
Speed / mate needed	Slower; a mate is needed	Fast; no mate needed
Main advantage	Variation helps survival if the environment changes	Fast and only one parent needed
Main disadvantage	Needs two parents; takes more time/energy	No variation — all clones share the same weaknesses

A quick memory hook for the four core rows:

1. Parents: sexual = 2, asexual = 1.
2. Gametes: sexual = yes (fuse), asexual = no.
3. Division: sexual = meiosis, asexual = mitosis.
4. Offspring: sexual = varied, asexual = identical clones.

Exam tip. If a table is given with one column filled in, mirror it exactly. For example, if "two parents" is written under sexual, write "one parent" under asexual — opposites, in the same wording.