Types of Reproduction

 

There are 2 types of reproduction in nature:

1. Sexual

2. Asexual

 

Sexual reproduction is the fusion of gametes (a sperm and an egg) from 2 parents. Asexual reproduction is the cloning of 1 parent, not involving gametes or multiple organisms.

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Meiosis is a key process in sexual reproduction. You need to know the steps required for it to happen:

1. DNA copied in a diploid cell

2. Cell divides twice → 4 haploid gametes  

3. All genetically different

(diagram)

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A diploid cell is a cell with the normal amount of chromosomes - 23 pairs (46 in total). 

A haploid cell is a cell with half that number of chromosomes - only 23 in total.

 

The haploid gametes (sperm and egg cells) can then combine during fertilization to make a regular diploid cell. If meiosis did not happen, the fertilized egg would have twice as much DNA as it should.

 

 Fertilisation → 23 + 23 = 46 (diploid) → embryo → mitosis + differentiation

 

You need to be aware of the pros and cons of each type of reproduction:

 

Sexual  

• Variation → survival if environment changes  

• Selective breeding → better crops

• Slower

• Mate Required

 

Asexual  

• Fast  

• No mate needed  

• Many offspring in good conditions

• No variation so could result in mass extinction if environment changes

 

Some organisms use both sexual and asexual reproduction:

• Malaria parasite → asexual in human, sexual in mosquito  

• Fungi → spores (asexual), sex for variation  

• Plants → seeds (sexual), runners/bulbs (asexual)