Sunday, January 21, 2007

Mausoleum of Maussollos

In 377 BC, Halicarnassus was capital of a small kingdom along the Mediterranean coast of Anatolia. It was in that year the ruler of this land, Hecatomnus of Mylasa, died and left control of the kingdom to his son, Mausolus. Hecatomnus, a local satrap to the Persians, had been ambitious and had taken control of several of the neighboring cities and districts. Next to Mausolus and Artemisia he had several other sons and daughters: Ada, Idrieus, and Pixodarus. Mausolus in his time extended the territory even further so that it finally included most of southwestern Asia Minor. Maussollos, with his queen and sister Artemisia, ruled over Halicarnassus and the surrounding territory for 24 years. Maussollos, though he was descended from local people, spoke Greek and admired the Greek way of life and government. He founded many cities of Greek design along the coast and encouraged Greek democratic traditions.

Maussollos decided to build a new capital, a city as hard to capture as it was magnificent to look at. He chose the town Halicarnassus. If Mausolus' ships blocked a small channel, they could keep all enemy warships out. He started making Halicarnassus a fit capital for a warrior prince. His workmen deepened the city's harbor and used the dredged up sand to make protecting arms in front of the channel.

Monday, January 08, 2007

Fraternal twins

Fraternal twins usually occur when two fertilized eggs are implanted in the uterine wall at the same time. The two eggs form two zygotes, and these twins are therefore also known as dizygotic as well as "biovular" twins. When two eggs are independently fertilized by two different sperm cells, fraternal twins result.

Dizygotic twins, like any other siblings, have a very small chance of having the exact same chromosome profile, but most likely have a number of different chromosomes that distinguish them. Like any other siblings, fraternal twins may look very similar, particularly given that they are the same age. However, fraternal twins may also look very different from each other. They may be a different sex or the same sex. Mixed-race twins, or twins born to parents of mixed racial origin, can vary considerably in their skin colouration and other features.

Monday, January 01, 2007

Cellular differentiation

Cellular differentiation is a concept from developmental biology describing the process by which cells acquire a "type". The morphology of a cell may change considerably during differentiation, but the genetic material remains the same, with few exceptions.

A cell that is able to differentiate into many cell types is known as pluripotent. These cells are called stem cells in animals and meristematic cells in higher plants. A cell that is able to distinguish into all cell types is known as totipotent. In mammals, only the zygote and early embryonic cells are totipotent, while in plants, many differentiated cells can become totipotent with simple laboratory techniques.

In most multicellular organisms, not all cells are alike. For example, cells that make up the human skin are different from cells that make up the inner organs. Yet, all of the different cell types in the human body are all derived from a single fertilized egg cell through differentiation.