In this article we will discuss about the role of meiotic divisions in reduction of chromosomes. The somatic (body) cells in multicellular animals have, as a rule, a diploid or double number of chromosomes; that is, apart from some exceptions due to the presence of sex chromosomes, every kind of chromosome in the set is represented by a pair of [...]
In this article we will discuss about the gastrulation and the formation of primary organ rudiments in fishes. In fishes the yolk formed in the oocytes during oogenesis initially does not differ substantially from the yolk in amphibian oocytes and eggs. It consists of yolk platelets lying in the cytoplasm and intermingled with other cytoplasmic components (mitochondria and the like). [...]
The function of the spermatozoon, for which its whole organization is adapted, is to reach the egg and, by fusing with the egg, to cause the egg to start developing and to transmit to the developing embryo the paternal genes. In most cases this means that the spermatozoon must have a high degree of mobility, and in fact, the organization [...]