modes of reproduction

• Asexual reproduction


  the process resulting in the production of genetically identical offspring from one parent
• mitosis


  type of a cell division giving rise to genetically identical cells in which the chromosome number is maintained
• why is mitosis important ?

  asexual reproduction, growth in multicellular organisms, repair of damaged tissues
• why is mitosis important in growth of multicellular organisms ?

  new cells must be produced by mitosis
• why is mitosis important in the repair of damaged tissues ?

  new cells are produced by mitosis to replace cells that are dead or damaged
• examples of asexual reproduction in plants

  stem tuber, rhizome, runner
• advantages of asexual reproduction

  • only 1 parent is needed
  • fusion of gametes is not required
  • all beneficial qualities are passed on to the offspring
  • producing offspring is faster than sexual reproduction
• disadvantages of asexual reproduction

  no genetic variation
• why is having no genetic variation a disadvantage ?

  when the offspring has no genetic variation to its parent, the species are not well adapted to changes in the environment. for example, if the parent does not have resistance to a particular disease, the offspring would also not have the resistance to the disease, meaning the whole population of plants could be wiped by a particular disease
• sexual reproduction


  process involving the fusion of nuclei of male and female gametes to form a zygote and the production of genetically dissimilar offspring
• homologous pairs of chromosomes

  one chromosome inherited from the male parent and one chromosome inherited from the female parent which have the same shape, size and the same sequence of genes
• meiosis


  type of cell division that gives rise to genetically dissimilar cells in which the chromosome number is halved due to the separation of homologous chromosomes
• meiosis: each gamete contains half the number of chromosomes as the parent cell
• a haploid cell is a cell with one set of chromosomes
• a diploid cells is a cell with two sets of chromosomes, one set from the male parent and the other from the female parent
• formation of gametes involves the process of meiosis
• why is meiosis important ?

  • forms haploid gametes
  • produces gametes that are genetically dissimilar
• how does meiosis produce haploid gametes ?

  during meiosis, each pair of homologous chromosomes in the parent nucleus separates to form the daughter cells which only receives one copy of the homologous chromosomes.

  during fertilisation, when the nucleus of the male gamete fuses with the nucleus of the female gamete, the normal diploid number of chromosomes is restored in the zygote.
• why is meiosis important in producing genetically dissimilar

  the greater the genetic variations, the better the species is adapted to changes in the environment. If organisms of the same species are varied, it is unlikely that a change in the environment will destroy the whole species. those that survive the change in environment will pass on their favourable genes to their offspring
• advantages of sexual reproduction

  • offspring may inherit beneficial qualities from both parents
  • there is genetic variation in the offspring that is better adapted to changes in the environment
• disadvantages of sexual reproduction

  • 2 parents required (except in plants with bisexual flowers)
  • fusion of gametes is required
  • this method is slower than asexual reproduction
• asexual reproduction requires only one parent while sexual reproduction requires two parents (except plants with bisexual flowers)
• asexual reproduction offspring are genetically identical to the parent while sexual reproduction offspring are genetically dissimilar to the parent
• asexual reproduction is relatively quicker in producing an offspring while sexual reproduction is a slower method of producing offspring