Sexual Reproduction

Contents Sexual reproduction Events in sexual reproduction Gastrulation Pre-fertilization events Organogenesis Fertilization Parturition Post fertilization events Mammalian reproductive cycles Embryogenesis Oviparous & viviparous animals Parthenogenesis Ovoviviparous animals Phases of life cycle Agieng and senescence Sexual reproduction . It is found in almost all the animals, plants and other life forms including fungi, bacteria and protists. A bi-parental process. Male and female gametes are formed. Germ cells act as reproductive units. Fertilization of male and female gametes occurs in order to obtain the Zygote. During meiosis, haploid gametes are produced from diploid germ cells. Produces their offspring less rapidly. Prominent male and female reproductive organs are required. Events in sexual reproduction Pre-fertilization events Fertilization Post-fertilization events Pre-fertilization events Gametogenesis Spermatogenesis Oogenesis . In most of the organisms male gamete is motile & the female gamete is stationary. In aquatic plants gamete transfer takes place through water. Male gametes are produced in very large number because a large number of male Gamete Transfer Gamete gametes are lost during transport. Fertilization . It is complete permanent fusion of two gametes from different parents or from the same parent. It results in the formation of a single celled, diploid zygote. It is of two types: External fertilization Internal fertilization Post fertilization events Zygote . Zygote is the vital link that ensures continuity of species between organisms of one generation and the next. Every sexually reproducing organism, including human beings begin life as a single-cell the zygote. Embryogenesis . Process of development of embryo from zygote. During embryogenesis, zygote undergoes : Mitotic cell division Cell differentiation Gastrulation Organogenesis Embryogenesis On the basis of development of zygote, animals are grouped Animals Oviparous Viviparous Ovoviviparous Oviparous & viviparous animals Oviparous animals Viviparous animals Animals that produce eggs that mature Animals that give birth to developed and hatch after being expelled from the live young individuals body Lay either fertilized or unfertilized egss Give birth to young individuals May undergo internal or external Undergo internal fertilization fertilization The development of zygote occurs The development of the zygote occurs outside the female inside the female The embryo receives nutrients from the The embryo receives nutrients from the yolk mother The chances of survival are less The chances of survival are more Birs,reptiles,amphibians,mostfish,insect Examples include most mammals s,are examples Ovoviviparous animals . These produce eggs, but instead of laying the eggs,the eggs develop within the mother’s body. The eggs hatch within the mothers body. Embryo get nutrition from yolk stored in egg. Examples include some sharks [such as the barking shark],scorpions. Gastrulation It is formation of three germ layers: . Ectoderm . Mesoderm . Endoderm Organogenesis It is formation of different organ systems from the three germ layers. Endoderm [internal layer] Lung cells [alveolar cell], Thyroid cells , Digestive cells [ pancreatic cell ] . Mesoderm[middle layer] Cardiac muscle cells, Skeletal muscle cells ,Tubule cell of the kidney Red blood cells , Smooth muscle cell [in gut] . Ectoderm[external layer] Skin cells of epidermis, Neuron on brain, Pigment cells Parturition It is process of giving birth to the baby. Parthenogenesis . Development of an egg into complete individual without fertilization. It is of two types Natural parthenogenesis Artificial parthenogenesis Phases of life cycle Juvenile phase/vegetative phase It is the period of growth between birth upto reproductive maturity. Reproductive phase/Maturity phase During this, the organism reproduces Senescent phase It is beings at end of reproductive phase when degeneration sets in structure and functioning of body. Aging and senescence Agieng. Gradual and spontaneous change, resulting in maturation through childhood and adolescence, and then decline through middle and late age. Senescence. The process by which the capacity for cell division, growth and function is lost over time. .

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