A chromosome deletion is a form of chromosome mutation. Chromosome mutations are due to changes in the structure of a chromosome, as opposed to gene mutations, which are changes within the chemical makeup of a chromosome. Chromosome mutations can actually be detected by looking at the DNA through a microscope. Mutations are changes in the DNA and they can have negative or positive consequences.
Within the nucleus of living cells, DNA is found in strands called chromosomes. Each type of organism has a specific number of chromosomes within its cells. For example, humans have 46 chromosomes, or 23 identical pairs. Along the chromosomes, genes specify the characteristics for the cells and ultimately the organism. Any mutation that occurs to a chromosome will affect this genetic information.
When a chromosome deletion occurs, part of a chromosome is removed, or deleted. Most of the time, the chromosomes can be found as long thin strands of DNA in the nucleus. They are all wound round each other, so there are plenty of opportunities for interactions with other chromosomes and with themselves.
During a chromosome deletion, the chromosome breaks in two different places. When the pieces join back together, the end pieces are attached and the middle piece is dropped out. This middle piece of the chromosome has now been deleted. Depending on what genetic information is carried on the deleted piece of the chromosome, the effects can be very serious. In some cases, this type of deletion can be lethal.
When a chromosome deletion occurs, the genes in the deleted piece are all but lost to the cell. As they are no longer a part of the chromosome, they will not go through the processes of transcription and translation, so the appropriate proteins will not be produced. Also, should the cell survive and replicate, that piece of DNA will not be copied, so all subsequent cells will also have this mutation. This type of mutation will have a profound effect on how the organism continues to develop. Actually, all but the shortest chromosome deletions are lethal to the cell.
Depending on the size of the chromosome deletion, it may be seen through a microscope. As chromosomes are found in identical pairs, one from the father and one from the mother, the two pairs can be compared. If there is a significant deletion to one of the pair, it will look different to its partner. In this way, where the deletion occurred can also be determined.
There are many different human chromosome disorders that are caused by a chromosome deletion. There are also many different symptoms and severity of symptoms depending on which chromosome was deleted and how much. Examples of disorders caused by chromosome deletions are cri-du-chat and some cases of Duchenne muscular dystrophy.