Invertebrate Reproduction

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Invert reproduction

Asexual

  • Fission (Budding)
    • formation of diploid individual by detachment of cells derived by mitosis, and subsequent differentation to form an adult
    • Common to soft bodied inverts - porifera, cnidaria, platyhelminthe
    • Many inverts undergo incomplete fission to form colonies
  • Apomixis
    •  formation of diploid individual from single cell derived by mitosis
  • Polyembryony
    • Multiple embryos form from 1 sexually formed blastula 
      • found in bryozoa, some insects, and the armadillo
  • Larval Cloning
    • Larvae undergo fission to produce small clone
      • Found in echinoderms
  • Some organisms - both sexual AND asexual reproduction
    • Obelia - gametophyte (medusa) produced by meiosis, so is haploid. budding used (asexual)
      • gametes produced by these gametophytes produced via mitosis, sperm + egg = sexual reproduction. forms polyp which grows + produces medusa buds.
  • Parthenogenesis
    • formation of individual from unfertilised egg
    • common to cladocerans, rotifers, aphids
      • phylum Rotifera - common, but obligate parthenogenesis rare
    • can also undergo sexual reproduction

Sexual

  • Dominant in inverts
  • Disadvantages
    • Half genome perpetuated
    • Breaks down good gene combos
    • Costs + risks of courtship
    • Time requirements
    • Fertilisation needed
  • Advantages
    • Helps species withstand environmental change thus reduces extinction rates
    • Allows evolution to occur faster
    • Enables large number of deleterious mutations to be removed from population
  • Breeding patterns
    • many different types
    • classified on number broods per lifetime and frequency of occurance
      • Semelparity - breeding occurs once a lifetime
      • Iteroparity - breeding occurs several times a lifetime
  • Sex determination
    • Maternal
      • Females produce 2 egg types
        • Large - develop into female
        • Small - develop into male
      • Dwarf males produce 2 types sperm
        • X sperm - fertilises large female eggs
        • O sperm - fertilises small  male eggs
      • Sex ratio determined by number of female and male eggs - governed by adult female
      • EXAMPLEDinophilus gyrociliatus
    • Genetic
      • Females have ** chromosomes
      • Males have XY chromosomes
      • All offspring…

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