Chromosomal Abnormalities in Humans

Chromosomal Abnormalities in Humans

A structure found inside the nucleus of a cell. It is made up of proteins and DNA organized into genes. It is passed from parents to offspring. Changes in chromosome parts, whole or set are known as chromosomal aberrations.

Chromosomal Disorder in Humans

Any syndrome characterized by malformations or malfunctions in the body system, and caused by abnormal chromosome number. In most cells, humans have 22 pairs of chromosomes and two sex chromosomes for a total of 46.22 pairs are autosomes. Any variation from this pattern causes abnormalities.

In chromosomes there are structural changes and numerical changes.

1. Chromosomal disorder due to numerical abnormalities

These disorders occur due to changes in the number of chromosomes present.This is following types.

1. Aneuploidy: It is the presence of an abnormal number of chromosomes in a cell like a human cell having 45 or 47 chromosomes instead of the usual 46.It originates during cell division when the chromosomes do not separate properly between the two cells.

Example: 1. Trisomy: The cell has one extra chromosome.

• Monosomy: The cell has one chromosome less.

Example: Abortion during pregnancy, Down syndrome and Turner syndrome.

Euploidy:

It is mostly occurs in plants. The euploidy is change in the complete set of chromosome.

1. Haploid: loss of one set of the chromosome.
2. Polyploid: Add of one or more set of chromosomes.

The chromosomal disorder due to structure abnormalities

It occurs due to a large set of genes are deleted, duplicated or rearrange causing structural changes in the chromosome.

1. Deletion: Any number of nucleotides can be deleted, from a single base to an entire piece of chromosome. It occurs during cell division.
2. Wolf-Hirschhormsyndrome: it is caused by partial deletion of the short arm of chromosome 4.
3. Jacobsen syndrome: The terminal 11q deletion disorder.
   1. Duplications: The portion of the chromosome has been duplicated, resulting in extra genetic material. The extra segment can be arrange in many ways

1. Tandem duplication 2. Reverse tandem 3.Displaced duplication 4.Transposed duplication. Example is fragile X.

• Translocation: That is a chromosomal segment is moved from one position to another, either within the same chromosome or to another chromosome. It can cause difficulties in the development of egg, sperm or zygote

Example:  Reciprocal translocation and Robertsonian translocation.

• Inversion: An inversion occurs when a single chromosomes undergoes   breakage and rearrangement with paracenter.

Types:  paracentric and pericentric.

• Insertion: A portion of one chromosome has been deleted from its normal place and inserted into another chromosome.