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.

• 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

• Klineefelter’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.