What Is Reproduction?• In a nutshell, reproduction is the creation of a new individual or individuals from previously existing individuals. In animals, this can occur in two primary ways: through asexual reproduction and through sexual reproduction. Lets look at asexual reproduction.
Asexual Reproduction• In asexual reproduction, one individual produces offspring that are genetically identical to itself. These offspring are produced by. There are many invertebrates, including sea stars and sea anemones for example, that produce by asexual reproduction.
Types of Asexual Reproduction• Budding - an offspring grows out of the body of the parent.• Gemmulation - a parent releases a specialized mass of cells that can develop into an offspring.• Fragmentation - the body of the parent breaks into distinct pieces, each of which can produce an offspring.• Regeneration - if a piece of a parent is detached, it can grow and develop into a completely new individual.
Sexual ReproductionIn Sexual Reproduction, Two Individuals ProduceOffspring That Have Genetic Characteristics From Both Parents. Sexual Reproduction Introduces New Gene Combinations in a Population.
Gametes•In Animals, Sexual Reproduction Encompassesthe Fusion of Two Distinct Gametes to Form aZygote. A Type of Cell Division Called MeiosisProduces Gametes. The Gametes Are HaploidWhile the Zygote Is Diploid. In Most Cases, theMale Gamete, Called the Spermatozoon, IsRelatively Motile and Usually Has Flagella. On theOther Hand, the Female Gamete, Called theOvum, Is Non-motile and Relatively Large inComparison to the Male Gamete.
Types of Fertilization•Oviparity – internal fertilization, deposited outside thebody to complete development•Oviviparity – internal fertilization, embryo stillnourished by yolk•Viviparity – internal fertilization, nourished directlyfrom mothers blood and later given birth
Patterns and CyclesReproduction and Is Subject to Certain Patterns andCycles Which Are Oftentimes Linked toEnvironmental Conditions, Which Allow Organismsto Reproduce Effectively. For Example, ManyAnimals Have Estrous Cycles That Occur DuringCertain Parts of the Year So That Offspring CanTypically Be Born Under Favorable Conditions.These Cycles and Patterns Can Be Controlled byHormonal Cues As Well As Other Seasonal CuesLike Rainfall. All of These Cycles and Patterns AllowOrganisms Maximize the Chances of Survival for theResulting Offspring.
Embryonic Development•Gestation Period lasts about 9 months•Divided into fetal and embryonic period•Embryonic period starts with fertilization and lasts 8 weeks•Fetal period lasts 6 ½ months
Stages of development• Fertilization - Includes penetrated oocyte, ootid, & zygote. Pronuclei appear.• Cleavage-Series of Cell Division• Gastrulation - Morphogenetic movements to form primitive germ layers• Organogenesis – Primary organs formed