Zoology chap 6

• Reproductive process


  Life springs from reproduction of preexisting life
• Forms of reproduction


  • Binary Fission
  • Multiple Fission
  • Budding
  • Gemmulation
  • Fragmentation
• Binary Fission


  The body of the unicellular parent divides by mitosis into two approximately equal parts
• Multiple Fission


  The nucleus divides repeatedly before division of the cytoplasm, producing many daughter cells simultaneously
• Budding


  Unequal division of an organism where a new individual arises as an outgrowth from its parent, develops organs, and then detaches. Prominent in cnidarians
• Gemmulation


  Formation of a new individual from an aggregation of cells surrounded by a resistant capsule (gemmule). Found in freshwater sponges
• Fragmentation


  When a multicellular animal breaks into two or more parts, with each fragment capable of becoming a complete individual. Seen in anemones and hydroids
• Asexual Reproduction


  Production of individuals without gametes. Offspring have the same genotype as the parent (clone)
• Examples of asexual reproduction

  • Bacteria
  • Unicellular eukaryotes
  • Many invertebrate phyla
  • Amoeba/Arcella
  • Trypanosome
  • Flagellate
  • Paramecium
  • Epulopiscium
  • Stanieria
  • Bdellovibrio
  • Planctomytes
• Bisexual Reproduction


  Production of offspring formed by the union of gametes from two genetically different parents. Parents are of different sexes, male and female
• Hermaphroditism


  Condition of having both male and female organs in the same individual
• Parthenogenesis


  Development of an embryo from an unfertilized egg or one in which the male or female nuclei fail to unite following fertilization
• Sexual Reproduction


  Production of individuals by gametes. Two parents with special germ cells that unite to produce a genetically unique individual
• Gametogenesis


  Production of mature gametes. Includes Spermatogenesis (gametogenesis in testis) and Oogenesis
• Sex Determination


  At first, gonads are sexually indifferent. In mammalian males, gametogenesis occurs in the testis
• Genital ridges


  Appearance of the gonads during early embryonic development
• Primordial germ cells


  Precursors of germ cells
• Gonads


  Primary organs that produce sperm and eggs and sex hormones
• Early embryonic development


  Primordial germ cells are precursors of germ cells
• Sex Determination


  At first, gonads are sexually indifferent
• Gametogenesis in mammalian males

  Production of mature gametes
• Spermatogenesis


  Gametogenesis in testis
• Oogenesis


  Gametogenesis in ovaries
• SRY


  The male-determining gene
• DMRT1


  Doublesex And Mab-3 Related Transcription Factor 1
• Classic experiments performed in rabbits provide support for the idea that the female is the default sex during development
• Fertilized eggs development


  In the oviduct or uterus with embryos deriving their nourishment directly from the mother
• Reproductive Patterns


  • Oviparous
  • Ovoviparous
  • Viviparous
• Oviparous


  Lay their eggs outside their body
• Viviparous


  Give live birth
• Reproductive Systems


  Consist of primary organs (gonads) and accessory organs
• Endocrine events that orchestrate reproduction

  Reproduction in vertebrates is usually a seasonal or cyclic activity
• Sexual reproductive process


  Controlled by hormones (hypothalamus)
• Principles of Development


  Developmental Biology encompasses the emergence of order and complexity during the development of a new individual from a fertilized egg, and the control of this process
• Developmental Theories


  • Preformation
  • Epigenesis
• Fertilization is the union of male and female gametes to form a zygote
• An egg cell is 200x as large as a somatic cell
• Sperm is approximately 1/50 the size of a somatic cell
• Contact recognition between egg and sperm


  Occurs through species-specific interactions
• Polyspermy is the entrance of more than one sperm