Chromosomal Disorders: Principles of Inheritance And Variation Class12

CBSE Class-12 Principles Of Inheritance And Variation - Chromosomal Disorders: The chromosomes are thread-like structures that are mainly present in the nucleus which carries the hereditary information of genes that are passed from the parents to the offspring. Due to some irregularities of cell division, alteration in the number or structure of chromosomes may happen.

The disorders which are caused due to the absence or abnormal arrangements of one or more chromosomes are known as Chromosomal Disorders. The changes in one chromosome part of whole chromosomal sets are known as chromosomal aberrations.

Chromosomal Disorders in Humans

The human cell consists of 46 chromosomes as 23 pairs out of which 22 pairs are the autosomes and 1 pair is the sex chromosome. The change in the structure or numerical values in chromosomes is called Chromosomal Disorder.

Chromosomal Disorders Due to Numerical Abnormalities

Aneuploidy

This kind of condition occurs due to the nondisjunction of chromatids when the chromatids fail to separate during cell division. In this, there is loss or gain of chromosomes occurs. In this one gamete consists of two copies of one chromosome and the other consists of no chromosomes.

• Trisomy: The cell consists of one extra chromosome (2n+1).
• Monosomy: The cell consists of one less chromosome (2n-1).

They occur due to the nondisjunction of autosomes therefore sex chromosomes or chromosome1-22.

Chromosomal Disorders Due to Aneuploidy

They are genetically inherited disorders caused by abortion during pregnancy.

• Down's Syndrome: This is a genetic disorder that is caused due to the presence of an additional copy of chromosomes of number 21. This disorder was described by Langdon Down. The individual who is affected is short-statured with a small round head, partially open mouth, and furrowed tongue, the palm is broad. The physical, mental, and psychomotor development is retarded.
• Turner's Syndrome: This disorder is caused due to the absence of one of the X chromosomes therefore 45 with X0. This type of female is sterile as ovaries are rudimentary. It lacks other secondary sexual characters.
• Klinefelter's Syndrome: This is a genetic disorder caused due to the presence of X chromosomes which results in a karyotype of 47, XXY. The individuals who are affected have masculine development. These individuals are sterile.
• Edward's Syndrome: The symptoms consist of multiple malformations in fingers, lower jaw, skull, face, and fingers. They can't live more than 3-4 months.
• Patau Syndrome: The symptoms of this syndrome consist of the individual can rarely live for more than a few months, individuals are mentally retarded, and serious defects in the eyes, brain, or kidney.
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