Chromosomal Abnormalities

The nucleus within a cell contains chromosomes which are composed of DNA which encodes genes

Chromosomes are single pieces of coiled DNA that contain sequences of nucleotides that encode our genes. Genes are coding sequences or sets of instructions that tell our bodies how to develop and function. The typical number of chromosomes in our cells is 46: 23 which come from the biological mother (egg) and 23 come from the biological father (sperm) therefore one has two copies of each chromosome.

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.

An example of reciprocal translocation. One fragment of chromosome 4 attaches to a fragment of chromosome 20 and another fragment of chromosome 4 attaches to another fragment of chromosome 20.

Chromosomes are found in the nucleus of our cells. Cells of many different kinds (i.e. liver cells, blood cells, skin cells) compose the different tissues of our bodies.
Chromosomal Abnormalities come in two categories: numerical and structural. Numerical abnormalities occur when an individual is missing a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy). Structural Abnormalities occur when the structure of the chromosome is altered by deletion, duplication, translocation, inversions and rings.

Chromosomal abnormalities occur through errors in cell division which can be either meiosis or mitosis.  These errors can potentially delete anywhere from 1 gene to an entire arm of a chromosome.  Therefore, the effects of each chromosomal abnormality can vary from severe to subtle or from many side effects to hardly any side effects in the individual.

Chromosome abnormalities usually result from an error in cell division. Meiosis is the cell division that the egg and sperm go through when they are developing. Normally, meiosis causes a halving of chromosome material, so that each parent gives 23 chromosomes to an offspring. When fertilization occurs, the normal 46 total number of chromosomes results. If meiosis does not occur properly, an egg or sperm could end up with too many chromosomes, or not enough chromosomes. A baby that ends up with an extra chromosome is a trisomy and a missing chromosome is referred to as a monosomy.  While pregnancies with a trisomy or a monosomy may go to full-term and result in the birth of a child with health problems, it is also possible that the pregnancy may miscarry.

While there are many types of chromosomal abnormalities ranging from severe to less compromising; this page is devoted to giving the reader a comprehensive view of three abnormalities that represent both numerical and structural sorts.


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