The threadlike structures found in a nucleus are called chromosomes. Chromosomes are found in all of the body's cells except for red blood cells, which are referred to as anuclear. They are composed of DNA that carries genetic information.
The largest organelle that is only visible with the light of a microscope is a nucleus. Some cells have multiple nuclei ranging from two to 50 nuclei and are referred to as multinucleated. Some liver cells and skeletal muscle cells are examples of multinucleate cells. The function of the nucleus is gene expression, processing of pre-mRNA and cell compartmentalization. Chromosomes cannot be viewed under a microscope unless the cell is dividing. Every chromosome has a point where the chromosome divides into two sections referred to as the centromere.
There are 46 chromosomes in the human body. Sometimes, chromosome abnormalities happen, but with today's science we have been able to diagnose these rare disorders. The most common numerical chromosome disorder is Down syndrome. Down syndrome is a type of trisomy, known as Trisomy 21, and happens when 47 chromosomes exist. Structural disorders occur spontaneously and can include Robertsonian translocations, insertions, translocations, balanced reciprocal translocations and unbalanced translocations, rings and more. Genetic testing is offered in the first trimester and a number of genetic conditions are tested for such as Trisomy 21 and 18, cardiac disorders or any fetal abnormalities.