Read the summary and the most important questions on Human and Animal biology I

• E-learning I

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• What is meant by the "animal part" in a frog egg?

  The animal part is the less heavy part (topmost) of an egg and contains mostly cytoplasm and the nucleus. This half of the egg contains the most pigment and thus has a darker colour.

• What is meant with the "vegetal part" of an egg?

  The vegetal part is located at the bottom of the egg, it is heavy and contains the yolk granula.

• What is the egg axis?

  The egg axis is an axis that runs from the animal pole to the vegetal pole of the egg.

• What is the animal pole of an egg?

  Recognisable by the pigment, but also a polar body that may be found there. (cytoplasm and nuclear material)

• What important chages in the egg cell are caused by fertilisation?

  • Completion of meisosis
    
  • Fusion of paternal and maternal genomes
  • Changes to the egg cell membrane (becomes imprenetrable for sperm cells)
  • Increse of calcium concentration in the cytosol, leading to activation of the egg cell
  • Following activation, rotation of the cell cortex occurs, resulting in development of the grey crescent.

• What happens to the outer layer of the egg cortex after being penetrated by a sperm cell?

  The outer layer shifts 20 degrees in relation t the inner layer. This creates a lighter spot opposite of the penetration point in the egg cortex, this is called the grey crescent.

• Where does the sperm cell penetrate the egg cortex in relation to the animal pole?

  The sperm cel penetrates the egg at a distance of 30 degrees form the animal pole

• How is the first cleavage of an embryo formed?

  The plane through the animal pole and the penetration point divides the grey descent in two halves. This is the symmetry plane of the future emryo and the plane for the first cleavage.

• Where is the plane of the second cleavage and what does it contain?

  The plane of the second cleavage contains the animal-vegetal axis and is pendicular on the first cleavage.

• What are the two cells that are created by the meridional cleavages that do contain the grey crescent called?

  Dorsal cells