IGCSE Coordinated Science: Asexual and Sexual Reproduction

Asexual Reproduction

  • Asexual reproduction is defined as the the process resulting in the production of genetically identical offspring from one parent (From IGCSE syllabus).

Advantages:

  • No need for special gametes.
  • All good characteristics are passed on.
  • No need to expend time or energy on courtship:
    • Thus such a species will be difficult to exterminate because even if one organism is left, it can reproduce and sire a whole new colony.
  • Reproduction is swift and will allow an organism to colonise territory very quickly:
    • This is why bacterial infections can happen very quickly after contact with the original organism.
  • Reproduction also generates a greater number of offspring.
  • Very small chance of mutation:
    • Can be both good and bad.

Disadvantages:

  • Bad characteristics will be passed on to the offspring.
  • All offspring are clones thus a species cannot adapt to changing living conditions and so may die out as a result of said changing conditions (no variation):
    • If you are infected by bacteria and you see a pharmacist and take antibiotic drugs.
    • If these drugs work for one bacterium cell, they will end up killing all of the rest of the bacteria too since they are all genetically identical and so none of them will be able to resist the drug.
      • However, it is possible that during reproduction mutations occur causing a change in the bacteria which makes it resilient to antibiotic drugs which only target specific bacterium cells.
    • A parent with no resistance to a particular disease will mean that the child will have no resistance to said disease.
    • Causes more problems because of this.
  • Parent plant has to expend more energy during reproduction.

Sexual Reproduction:

  • Sexual reproduction is defined as the process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring (From IGCSE syllabus).

Advantages:

  • Such an organism can adapt to changing circumstance because offspring are not genetically identical to their parents thus at least some offspring will survive each change in living circumstances.
    • Causes fewer problems because of this.
    • This advantage is a major advantage of sexual reproduction and is very important.
    • This is caused by the mixing of the genetic information supplied by both parents.
  • Bad characteristics may not be passed on.
  • The fact that two parents exist means that the responsibility of bearing and raising any offspring is divided. This allows the offspring to potentially receive a better upbringing (note that this is dependent upon the species in question).
  • Sexual reproduction also usually generates fewer offspring; this is both an advantage and a disadvantage. It is an advantage in that fewer offspring means less competition for resources and for the attention of the parent (note that this is dependent on the species). It is a disadvantage in that fewer offspring decrease the chances of the species survival.

Disadvantages:

  • Good characteristics may not passed on.
  • Expending energy on courtship.
  • Expending energy on gamete transfer:
    • The process of gametes coming together is called fertilisation.
    • Gametes only contain half of the genetic makeup of the parent:
      • It is a haploid cell meaning that only half of the genes are present in said cell.
        • A human sperm and egg cell only contains 23 out of 46 chromosomes.
        • When fertilisation occurs a diploid cell (cell with all of the genes present) is created:
          • The 23 chromosomes pair up to do this.
        • The result is a zygote.
        • This is how the offspring becomes a mixture of the genetic information from both parents.
          • One exception to this is the formation of identical twins:
            • Because one egg cell and one sperm cell only are involved, both twins have the same genetic makeup.
      • Such cells include sperm cells, egg cells and pollen grains.
  • Expending energy on attracting something for gamete transfer:
    • Insect pollinated plants devote much energy to the development of flowers to attract pollinating insects.
  • Reproduction is slower and does not generate a large number of offspring.
  • Good chance of mutation:
    • Can be both good and bad.
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