Genbio 2: Animal and plants reproductive part.

• Growth is a stage of development characterized by an increase in size of an individual.
• Development involves formation of sex cells, zygote formation, subsequent stages in one’s life span. Development is terminated by death.
• Gametogenesis - a process which refers to the biological formation of gametes via a series of cellular division, differentiation, and genetic material reduction to achieve a haploid
• The formation and development of sperm cell are via spermatogenesis
• female counterpart, egg cell or ovum, is via oogenesis.
• Spermatogenesis - The precursor cell spermatogonium first divides and differentiates into two primary spermatocytes via mitosis. The spermatocyte undergoes first meiotic division giving rise to two secondary spermatocytes. Further, each secondary spermatocyte proceeds to second meiotic division giving rise to four spermatids that mature into sperms having an equal number of genetic material and cytoplasm.
• Oogenesis - The daughter cells produced from the two meiotic divisions do not receive an equal amount of cytoplasm primarily because almost all of the cytoplasm of the primary oocyte is concentrated only to one of its daughter cells. High concentration of cytoplasm in an ovum provides enough nourishment to the developing embryo after fertilization.
• Fertilization- The two gametes fuse together via fertilization which starts the development process. In animals, zygote(fertilized egg) formation occurs once a sperm cell successfully fused to an ovum, which in turn allows embryo development to take place.
• Cleavage - Fertilization initiates embryotic development allowing cleavage to take place. Cleavage is the rapid series of mitotic cell divisions of the developing embryo leading to multicellular ball mass. In mammals, this continuously happens as the embryo transverses the oviduct toward the uterus. Once more than 100 cells are present, the embryo is now a blastocyst, characterized by having a distinct inner cell mass, which eventually forms the fetus.
• Gastrulation - is the formation of three germ layers: ectoderm, mesoderm and endoderm. Each will give rise to specific tissues and organs.
• Organogenesis - is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal organs of the organism.
• ECTODERM(Outer layer)

  MESODERM (Middle layer)

  ENDODERM ( Inner layer)
• The mature, multicellular organism is a diploid sporophyte.