LBBBIO8 Activity 2

• Cell division is an important process in living organisms. It is involved in the multiplication of cells for growth and development of an organism.
• Cell division can be viewed as a cycle, and can be arbitrarily, categorized into two stages: interphase and mitosis
• Interphase; the cell undergoes growth and prepare for cell division. Actual replication of the genetic material of DNA occurs in this phase, to ensure that each daughter cell would have a complete set of genetic material.
• During Interphase, cell has a distinct nucleus and an intact nuclear membrane.
• Chromatin: genetic materials inside the nucleus that appears as thin, thread-like structure.
• Nucleoli: these are dense, darkly-stained bodies formed by several chromosomal material that code for certain RNAs.
• Near the nucleus is the centrosome, which contains centrioles.
• M-Phase is the phase during which the cell divides. It is divided into four stages.
• Prophase:

  +the nuclear membrane starts to disappear

  +the chromatin fibers start to appear as coiled, thickened, condensed structure forming chromosomes.

  +Centrioles are seen in the opposite poles.

  +You can locate ray-like microtubule bodies called asters radiating around each centrioles and mitotic spindles forming between centrioles.

  +The nucleoli disappears.
• Metaphase:

  +chromosomes are aligned at the equatorial region of the nucleus (metaphase plate).

  +the replicated chromosomes are much shorter and condensed, readily recognized.

  +the chromosomes are made up of chromatids joined together at their central region called centromere.

  +A protein coat called kinetochore is found in each of the sister chromatid.

  +The spindle fibers are attached at the centromere of each chromosome.
• Anaphase:

  +chromatids are pulled apart toward the opposite poles.

  +can be differentiated into early and late stages depending on the distance travelled by the chromatids.

  +once the chromatids separate, these are considered as chromosomes reaching the opposite poles.
• Telophase:

  +cleavage furrow, a constriction of the plasma membrane at the region of the equatorial plate, starts to appear.

  +the nuclear membrane and the nucleolus start to reappear.

  +the chromosomes begin to uncoil and assume a thread-like appearance.

  +the asters and mitotic spindles disappear.

  +at late telophase, the cleavage furrow becomes more constricted, leading to formation of 2 daughter cells.
• Cytokinesis is the division of the cytoplasm usually occurs along with telophase.
• There are two types of development in organisms: phylogeny and ontogeny
• Phylogeny refers to the evolutionary history of an individual or group of individuals from its ancestor.
• Ontogeny refers to the developmental process that leads to the maturation of an embryo into an adult organism.
• Animal Embryology deals with the study of specific stage on the ontogenetic development of an animal, the embryo.
• The term embryo refers to the developing young from a fertilized egg to a form that is structurally similar to, but does not yet precisely resemble, the adult.
• Fertilization involves the union of the sperm and egg nuclei.
• Zygote is the appropriate term to use for the embryo as a result of fertilization.
• Cleavage is the process of transforming the single celled zygote into a multicellular entity. It involves a series of mitotic division, which transforms the zygotes to several cleavage cells or blastomeres.
• The first mitotic division results into two blastomeres or 2-cell stage.
• The second mitotic division yields 4-cell stage.
• The third mitotic division yields an 8-cell stage.
• The ball of cells that is formed as a result of these series of cell division is called morula.
• Smaller blastomeres are sometimes called micromeres and are situated at the animal pole.
• Larger blastomeres are called macromeres and are situated at the vegetal pole.
• Cytoplasm has granular appearance, usually dark-stained. The cytoplasm of the egg is filled with yolky material, which serves as nourishment for the developing embryo.
• This yolky material is concentrated in the vegetal pole.
• The area opposite the vegetal pole is the animal pole.
• The type of egg based on yolk distribution is referred to as telolecithal type.
• Blastulation is the process that involves an internal secretion of fluid by the blastomeres of the morula. It results in the formation of a fluid-filled cavity, the blastocoel or segmentation cavity.
• The embryo at the Blastulation is referred to as blastula.
• In blastulation, the layer of cells immediately surrounding the blastocoel forms the endoderm while the outer layer of cells form the ectoderm. At this stage, the embryo is characterized as didermic.
• Gastrulation is the stage that involves major cell movements and rearrangements to form the body plan characteristic of a species. These phenomena are commonly referred to as morphogenetic movements.
• 1.) micromeres

  2.) blastocoel

  3.) marginal zone

  4.) macromeres

  
• 1.) archenteron

  2.) blastocoel

  3.) yolk plug

  4.) dorsal lip of blastopore

  5.) ventral lip of blastopore

  
• 1.) neural fold

  2.) neural groove

  3.) notochord

  4.) lateral plate mesoderm

  5.) paraxial mesoderm

  
• 1.) neural fold

  2.) neural tube

  3.) notochord

  4.) gut

  5.) endoderm