Asexual Reproduction

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Outcome:
  • Biological advantages and disadvantages of asexual reproduction


Reproduction involves the formation of new life from a progenitor source, via either an asexual mechanism or a sexual mechanism

  • It can involve the production of new cells (i.e. daughter cells) or entirely new organisms (i.e. offspring)


Asexual Reproduction

Asexual reproduction involves the formation of offspring that are genetically identical to the parent

  • Advantages:  Only involves a single parent, so there is less of an energy cost involved (no need to find a mate and can occur quickly)
  • Disadvantages:  Offspring a genetically identical to parent (i.e. clones) – meaning there is no biodiversity or species richness


The mechanism by which asexual reproduction occurs is dependent on the type of organism involved

  • Examples of asexual reproductive processes include binary fission, fragmentation, budding, vegetative propagation or spore formation


Binary Fission

Binary fission is a rapid method of asexual reproduction employed by prokaryotic cells 

  • The circular DNA is first copied in response to a replication signal and then the two DNA loops attach to the membrane 
  • The membrane elongates and pinches off (cytokinesis), forming two cells with identical DNA molecules 
  • Certain eukaryotic organisms (e.g. Planaria and amoeba) may also reproduce asexually via a fission-like process


Budding

Budding involves the growth of cells on a parent organism, which separate from the parent to form an autonomous organism

  • This method of cloning occurs in species of Hydra, but is also common to many species of yeast (fungi).


Fragmentation

Fragmentation involves the growth of a new organism from a separated portion of a parental organism 

  • From the fragment, the offspring will develop to be morphologically identical to the parent 
  • Fragmentation is common to starfish, as well as certain species of annelid worms


asexual reproduction


Vegetative Propagation

Plants have the capacity for vegetative propagation, whereby sections of a plant can be induced to grow independently 

  • This is because all adult plants possess meristematic tissue which is totipotent (undifferentiated) 
  • Virtually all types of roots and shoots are capable of vegetative propagation


Spore Formation

Some species form spores via an alternating cycle of generations (e.g. certain non-flowering plants, fungi, algae and protozoa) 

  • A diploid plant will form a haploid spore (via meiosis) that will then germinate to form a haploid plant 
  • As the offspring was produced from a sole parent, it represents an asexual reproduction cycle (the gametophyte phase)
  • The haploid plant then produces gametes (via mitosis) which can fuse with another haploid gamete to form a diploid offspring 
  • As this offspring was produced from two parents, it will represent a sexual reproduction cycle (the sporophyte phase)


spore formation


Parthenogenesis

Parthenogenesis is a form of asexual reproduction in which an offspring develops from an unfertilised gamete 

  • There are different pathways by which this occurs, but it usually involves the production of a diploid egg cell by the female parent 
  • This process occurs in certain species of insects, fish and reptiles