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GROUP 4 Deletion :- Cytogenetics and causes

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DNA is a group of molecules that is responsible for carrying and transmitting the hereditary materials from parents to off-springs.  A Gene is a basic fundamental unit of DNA which codes for protein synthesis.  DNA is made up of genes, and Chromosomes are made up of DNA.

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Chromosomes are thread-like structures present in the nucleus. They are important as they contain the basic genetic material DNA.  These are present inside the nucleus, human beings have 46 chromosomes in their body.  These are arranged into 23 pairs, 22 pairs of autosomes and 1 pair of sex Chromosome.  The study of normal and mutated chromosomes and their behavior is called " Cytogenetics ".

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Chromosomal mutations or deletions are variations from the wild-type condition in chromosome number or chromosome structure. Chromosomal mutations can occur, or they can be induced by treatment with chemicals or radiation.  A deletion is a chromosomal mutation in which part of a chromosome is missing. A deletion starts where breaks occur in chromosome.  Breaks can be induced by agents such as heat, radiation (especially ionizing radiation;       viruses , chemicals, and transposable elements or by errors in recombination. Because a segment of chromosome is missing, deletion mutations cannot revert to the wild-type state.

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The process of spontaneously occurring deletion must include two chromosome breaks to cut out the intervening segment. If the two ends join and one of them bears the centromere, a shortened chromosome results, which is said to carry a deletion.  The deleted fragment is acentric; consequently it is immobile and will be lost.

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Hurnan karyotype shOW'ing abnorrnal chrornosomes
(blue) resulting frorn a reciprocal exchange Of parts Of
two nonhornologous chrornosornes.

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The loss of a segment of the genetic material in a chromosome is called Deletion. The two types of deletion are terminal and intercalary deletion.           1. Terminal Deletion:- When the deletion occurs at the end of the              chromosome it is called  terminal  deletion  eg . drosophila and maize.          2.Intercalary Deletion:- When the deletion occurs in the middle of the chromosome it is called intercalary deletion.

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A deletion mutation occurs when part of a DNA molecule is not copied during DNA replication. This uncopied part can be as small as a single nucleotide or as much as an entire chromosome. The loss of DNA during replication can lead to genetic disease or disorder. In point mutation, an error occurs in a single nucleotide.   A chromosome deletion is also possible, where an entire section of chromosome is deleted. This can involve any number of base pairs as long as it is more than one(that would be a point deletion). Sometimes an entire chromosome can be deleted as well. Whenever this happens, a number of genetic diseases or disorders can occur, which can be chronic, life long or fatal in some cases .

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The example of genetic syndrome caused by deletion is known as Cri du Chat.  The part of the 5 th  chromosome is missing or deleted. When genes are missing, there may be changes or errors in the development of the baby, since some of the instructions are missing. This syndrome is found in approximately one in twenty to fifty thousand life births in US.  The effect of the syndrome on the baby are such as high-pitched cry, poor muscle tone, small head size and low birth weight.  They also face problems in walking, language, feeding, hyper-activity, and severe intellectual ability.

GROUP 4 Deletion :- Cytogenetics and causes

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