At the smallest level of organization, the DNA wraps itself around small globular proteins called histones. Complexes of histones and DNA form nucleosomes, which appear as "beads" on the DNA strand. Chromatin refers to the decondensed DNA that has not formed separate chromosomes.
Ureter, the structure that carries urine from the kidney to the bladder is called Ureter
Answer:
Atoms are electrically neutral as a result of having an equal amount of positive (due to the protons) and negative (due to the electrons) charges on it.
An ion generally is an electrically unbalanced atom (i.e an atom with a net charge on it)
A negative ion called an anion is produced when an atom gains an extra electron from a neighboring atom, giving it an extra negative charge. This can be produced by ionization with a radioactive radiation or simply by dissolution.
A positive ion is called a cation and it is produced when an atom loses electron to a neighboring atom. The loss of this electron causes the positive charges to outweigh the negative charges in the atom. Cations can be produced by radioactive radiation ionization of an atom or by simple dissolution.
The subatomic particle that is negative is the 'electron'.
In the block to polyspermy, entry of the sperm's contents causes calcium ion levels in the oocyte's cytoplasm to rise, triggering the cortical reaction.
In biology, polyspermy describes the fertilization of an egg by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent.
The cell resulting from polyspermy, on the other hand, contains three or more copies of each chromosome—one from the egg and one each from multiple sperm. Usually, the result is an unviable zygote. This may occur because sperm are too efficient at reaching and fertilizing eggs due to the selective pressures of sperm competition.
The cortical reaction is a calcium-dependent exocytotic process in which the content of secretory granules is released into the perivitellin space immediately after fertilization, which serves to prevent polyspermic fertilization.
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