Rabu, 23 September 2009

sperma cell

A sperm cell is one of the most specialised cells in the animal body. They arise by repeated mitosis followed by meiosis to produce haploid immature sperm cells, each with a different genotype (if the process was meiosis followed by mitosis all the cells would have the same genotype). This is spermatogenesis. The sperm mature in the epidydimis, but they do not become fully mature until they reach the female oviduct. They have three separate regions.

The Head.

This has two important features. The acrosome contains lytic enzymes which are released when the sperm reaches an ovum. These enzymes digest the outer membrane of the egg, allowing penetration of the sperm. The head also contains a single set of chromosomes derived from the male. This will include either an 'X' or 'Y' chromosome, because of the way the XY separate during meiosis.

The Middle Section.

This part, immediately behind the head, contains numerous mitochondria. These respire sugars in the semen to generate ATP in order to provide the energy for movement of the tail.

The Tail.

This contains microfilaments running the length of the tail (arranged in the usual 9 + 2 system seen in Eukaryotic organisms). Rhythmic contraction of the filaments causes the tail to wave and move against the fluid environment, providing forward motion.

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