Chromosomal disorder - Down Syndrome, Turner syndrome Klinefelters syndrome, Cri chu dat syndrome

Chromosomal disorder is caused due to absence or excess or abnormal arrangement of one or more chromosomes.On the other hand, These disorders are also caused by the chromosomal aberration that occurs due to the deletion or insertion or translocation of chromosomes. Basically there are two prominent causes that lead to the chromosomal disorder.These are polyploidy and Aneuploidy.

Aneuploidy is  failure of segregation of chromatids during cell division and causes the gain or loss of chromosomes whereas Polyploidy is failure of cytokinesis after telophase stage of cell division results in an increase in a whole set of chromosomes in an organism.

Monosomy and Trisomy

Due to abnormal chromosomal arrangement, There is increase or decrease in the number of chromosomes in the normal genome. When chromosome number is increased termed trisomy and it is represented as 2n+1 and when chromosome number is decreased called monosomy. Monosomy is represented as 2n-1.

👌👌Remember - Down syndrome and klinefelter's syndrome  appear due to the trisomy whereas Turner syndrome appears due to the monosomy.

Example of Chromosomal disorder

Down syndrome-

It was first described by Langdon Down. This is caused due to a gain of extra copy of chromosome 21. It is also called  trisomy of the 21 chromosome. The symptoms of Down syndrome are - Affected individual is short with a small round head, furrowed tongue and partially open mouth. Broad palm with characteristic palm crease. Physical, psychomotor and mental development is retarded.

Turner syndrome -

Turner’s syndrome is caused  due to the loss of an X-chromosome in human females  therefore affected females have 45 chromosomes instead of 46 chromosome.The genetic constitution or karyotype of this syndrome is represented as XO. The symptoms of this disorders are - Females are sterile as ovaries are rudimentary.

Klinefelter's syndrome Klinefelter’s syndrome  occurs due to the presence of an additional copy of X-chromosome. The total number of chromosomes is 47.The genetic constitution or  karyotype of this syndrome is XXY. The affected individual is male but has female characters  due to the presence of an extra X chromosome. The symptoms of this disorder are - Gynecomastia and  individuals are sterile due to  low testicular growth, low production of testosterone. The syndrome may  cause reduced muscle mass, reduced body and facial hair, and enlarged breast tissue

Cri-du-chat syndrome

This syndrome is caused due to the  deletion of the short arm of chromosome number 5. The cri-du-chat syndrome, also known as cat's cry syndrome,

👌👌Remember  Cri du chat syndrome is also known as 5p  syndrome.

The affected  Infants have a high-pitched cry  like the sound of a cat. The symptoms of this syndrome are - mental retardation,  small head size, low birth weight, and weak muscle. The other symptoms in affected individuals are-  widely set eyes, low set ears, a small jaw, and a rounded face. Some children with cri-du-chat syndrome are born with a heart defect.

Philadelphia chromosome

This chromosomal abnormality takes place due to the translocation of chromosomes.

The Philadelphia chromosome forms when chromosome 9 and chromosome 22 break and exchange portions. This creates an abnormally small chromosome 22 and a new combination may cause chronic  leukemia.