Re: what is a cell pattern in an animal body and its organ system

I'm going to assume that you have heard about 'cell patterns' in bodies and organs within the context of development - this is where the term 'cell pattern' and 'pattern formation' are used in biology. Pattern formation refers to the way by which different types of cells in an embryo are produced in a regular spatial way. A few cells start out as a poorly defined 'blob' and through cell-to-cell interactions create well defined patterns and structures. Signals between cells let each cell know where the others are and thus where each cell itself is. The simplest type of signalling between cells is by the diffusion of a morphogenic (form changing) substance - usually along a gradient from high to low concentration. Slight differences in the genetic makeup of cells will allow them to respond to the different concentrations of the morphogen. Its best to understand this by looking at an example. Fruit-flys (with the mouthful of a scientific name - Drosophila) are often used to study development - they produce lots of babies and they are small enough to store lots in a lab! A fertilised egg looks pretty much like this:

You might notice it has no head or tail…the problem for this egg is to decide what cells are going to grow into the head and what will grow into the tail, i.e. what 'pattern' are the cells going to form? If you imagine a substance is produced at one end of the egg (it doesn't matter which end at this point) and it diffuses along a concentration gradient like this:

The local concentration controls the behaviour of cells according to how far they are from the source. The cells change and divide and form a pattern along the length of the egg-embryo.

Its now much more obvious from the pattern of cells which end of the original egg will be the head of the fruitfly!

The final pattern of cells and thus of the whole animal is built up from many combinations of bits of positional information determined by many gradients of morphogenic substances and genetic information specific to each cell type.