Chromosomes are not visible in the cell's nucleus – not even under a microscope – when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.
Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or "arms." The short arm of the chromosome is labeled the "p arm." The long arm of the chromosome is labeled the "q arm." The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.
Chromosomal aberrationChromosomal aberration is any abnormality in the chromosomes of a cell, such as a variation in the normal number or a change in the normal arrangement of the genetic material, which may produce an unexpected characteristic. Down's syndrome, for example, is associated with an extra chromosome. Some malformations have been associated with the absence of sections of certain chromosomes.
Related category• GENETICS AND HEREDITY
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