1. Sexual and Asexual Reproduction
Unit 2: Organisms and Evolution
Advanced Higher Biology
Miss A Aitken

2. Costs and Benefits Two forms of reproduction: Sexual Reproduction
Asexual Reproduction
Why do both forms exist?
They must exist because neither one is perfect for all situations. If it was perfect, only one would exist.

3. Asexual Reproduction vs Sexual Reproduction
Metabolic costs are lower – less energy required
Many identical offspring suited to the environment of the parent (clones)
Simple
Rapid
Lots of energy required as a special type of cell division needed (meiosis)
Only half of the population can actually produce offspring
Much slower than asexual reproduction

4. The Paradox of Sex
Why is sexual reproduction the most common way of reproducing?
Main problem – why do males exist?
They are unable to produce offspring themselves so only half of the population can actually have offspring – reducing effectiveness of population by 50%
Combining genetic material from mother and father disrupts successful genomes as only half of each’s genetic info is passed to the offspring.

5. Asexual Reproduction – Useful for Some
Asexual reproduction in prokaryotes
Bacteria and archaea (other single celled organisms) reproduce by asexual reproduction – they divide and make more of themselves. They can also carry out Horizontal Gene Transfer

6. Asexual Reproduction – Useful for Some
Asexual reproduction in plants
Many plants use asexual reproduction
Flowering plants use sexual reproduction but a wide range of asexual strategies have evolved as well including: bulbs, corms, tubers, runners and rhizomes.
Fungi and non-flowering plants sometimes use spores to disperse offspring.

7. Asexual Reproduction – Useful for Some
Asexual reproduction in animals
Extremely uncommon
Parthenogenesis is the name given to asexual reproduction in animals (literally means “virgin creation”)
Females produce offspring without the requirement for a male. The offspring are all female and are clones of the mother.
All animals which carry out parthenogenesis can also carry out sexual reproduction to produce males/variation.
More commonly found in cooler climates with low parasite density or diversity.

8. Conditions that Favour Asexual Reproduction
Producing identical offspring can be useful in a narrow and stable niche.
Aphids use asexual reproduction to quickly exploit a new food source
Useful for recolonising disturbed habitats – for example, buttercup plants use asexual reproduction to spread over an area of clear soil.