Asexual Reproduction Notes

Cambridge IGCSE Biology: Revision notes

Key facts

  • Asexual reproduction makes genetically identical offspring from one parent, with no gametes.
  • Sexual reproduction involves two parents, fertilisation and genetically different offspring.
  • Examples: runners and bulbs in plants, budding in yeast, binary fission in bacteria.
  • Asexual reproduction is fast and needs no mate, but gives no variation, so clones are equally vulnerable to disease.

Asexual reproduction

One parent produces genetically identical offspring, called clones.

If a question mentions 'one parent' and 'genetically identical offspring', it describes asexual reproduction. No gametes are involved and no fertilisation happens.

  1. 1

    One parent

    no gametes and no fertilisation

  2. 2

    Mitosis

    cells divide to make new cells with the same genes

  3. 3

    Genetically identical offspring

    clones of the parent

Asexual reproduction in outline.
  • Asexual reproductionone parent, genetically identical offspring

An organism produces offspring from one parent with no gametes. Are the offspring genetically identical to the parent?

Asexual or sexual

Sexual reproduction needs two parents and gametes, and gives genetically different offspring.

In sexual reproduction the nuclei of two gametes fuse to form a zygote. Gametes are made by meiosis; asexual reproduction involves mitosis only.

  1. 1

    Two parents

    each makes gametes by meiosis

  2. 2

    Fertilisation

    the nuclei of two gametes fuse

  3. 3

    Zygote

    divides by mitosis to form the embryo

  4. 4

    Genetically different offspring

    a mixture of both parents' genes

Sexual reproduction in outline.

Asexual

Parents:
One
Gametes and fertilisation:
None
Offspring:
Genetically identical to parent
Cell division:
Mitosis

Sexual

Parents:
Two
Gametes and fertilisation:
Fusion of two gametes forms a zygote
Offspring:
Genetically different
Cell division:
Meiosis to form gametes

Which cell division makes gametes for sexual reproduction?

Examples

Plants, fungi and bacteria all reproduce asexually in different ways.

A strawberry plant sends out a runner along the ground, and a plantlet forms at a node. It is genetically identical to the parent. Bacteria divide by binary fission and yeast grows buds.

  1. 1

    Genetic material copies

    the cell makes a copy of its DNA

  2. 2

    The cell grows longer

    the two copies move apart

  3. 3

    The cell divides

    two genetically identical cells form

Binary fission in bacteria.

Organism

Runners:
Strawberry
Bulbs:
Daffodil
Budding:
Yeast
Binary fission:
Bacteria

What happens

Runners:
Horizontal stem produces a new identical plant
Bulbs:
Bulb grows into a new identical plant
Budding:
New individual grows from the parent and detaches
Binary fission:
One cell divides into two identical cells

Which is an example of asexual reproduction?

Advantages and disadvantages

It is fast and needs no mate, but the lack of variation makes populations vulnerable.

In the wild, one parent is enough and a population can colonise an area quickly, but with no variation it may not survive a change or a new disease. In crops, all offspring have the same desirable features and it is cheap, but the whole crop is equally vulnerable to disease.

12345610203040506070xy864number of individuals
Illustrative values: if every cell divides each generation, numbers double each time, so one parent can colonise an area rapidly.

Advantage

In the wild:
One parent needed; rapid colonisation
In crops:
Same desirable features; fast and cheap

Disadvantage

In the wild:
No variation: may not survive change or disease
In crops:
Whole crop equally vulnerable to disease

Why is a crop of clones vulnerable to a new disease?

Try an exam question

Give two advantages and one disadvantage of asexual reproduction for a farmer growing strawberries.

[4 marks]

That's the notes covered.

Carry on to the next subtopic.