• Sexual reproduction is:

The process involving the fusion of the nuclei of two?gametes?to form a?zygote?(fertilised egg cell) and the production of offspring that are genetically different from each other

• Fertilisation is defined as the?fusion of gamete nuclei, and as each gamete comes from a?different parent, there is?variation?in the offspring

Gametes and zygotes

• A?gamete?is a sex cell (in animals: sperm and ovum; in plants: pollen nucleus and ovum)
• Gametes differ from normal cells as they contain?half the number of chromosomes?found in other body cells - we say they have a?haploid nucleus
• This is because they only contain?one copy of each chromosome, rather than the two copies found in other body cells
• In human beings, a normal body cell contains?46 chromosomes?but each gamete contains?23 chromosomes
• When the male and female gametes fuse, they become a?zygote?(fertilised egg cell)
• This contains the full?46 chromosomes, half of which came from the father and half from the mother - we say the zygote has a?diploid nucleus

Advantages and disadvantages of sexual reproduction

• Although there are some clear advantages of sexual reproduction (in comparison to asexual reproduction), there are also a few disadvantages of sexual reproduction

Advantages & Disadvantages of Sexual Reproduction Table

• Asexual reproduction is:

The process resulting in genetically identical offspring being produced from one parent

• Asexual reproduction does?not?involve?gametes?or?fertilisation
• Only one parent is required?so there is no fusion of gametes and no mixing of genetic information
• As a result, the offspring are?genetically identical to the parent and to each other?(they are clones)
• Many?plants?reproduce via asexual reproduction
• Bacteria?produce exact genetic copies of themselves in a type of asexual reproduction called?binary fission

Bacteria produce exact genetic copies of themselves in a type of asexual reproduction called binary fission

Advantages and disadvantages of asexual reproduction

• Whilst asexual reproduction has several advantages over sexual reproduction, it also has a few disadvantages

Advantages & Disadvantages of Asexual Reproduction Table

• The key differences between sexual and asexual reproduction include:
  • The?number of parent organisms
  • How?offspring are produced (the?type of cell division?required)
  • The?level of genetic similarity?between offspring
  • The possible?sources of genetic variation?in offspring
  • The?number of offspring?produced
  • The?time taken?to produce offspring

   

Comparing Sexual & Asexual Reproduction Table

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