CHROMOSOMES & KARYOTYPES

==Chromosomes== [image:http://i.imgur.com/HfYywrYl.jpg] Long sequences of DNA are found in the nucleus, coiled into structures called chromosomes. Chromosomes can contain many thousands of genes. [image:http://i.imgur.com/gpaR5sR.png?2] They are only visible just prior to cellular division when the DNA has been copied tightly coiled. At this stage of the cell cycle chromosomes have a "double sausage" appearance because they contain the two identical copies of each DNA strand. Each copy (half of the chromosome) is called a '''chromatid''' and the two chromatids are held together at point called a the '''centromere'''. ==Karyotypes== A karyotype is simply a picture of the chromosomes in a cell arranged according to size. A human cell has 46 chromosomes or 23 homologous pairs. If we looked at each homologous pair, we would find that one chromosome from each pair was inherited from the mother and the other from the father. Below is a karyotype from a normal male. [image:http://i.imgur.com/y0pVBwQ.png]