Most Common Chromosomal Disorders

Chromosomes are known long thread-like DNA molecules that are primarily responsible for determining the genetic characters of the organisms. Chromosomes are found inside the nucleus in animal and plant cells. On the other hand, bacteria like prokaryotic organisms contain chromosomes in the cytoplasm because of the absence of a nucleus.The genetic characters transferred by the chromosome alter for various reasons, which causes the disorder. Disorders of chromosomes can be caused by abnormalities in these chromosomes.Normally, humans contain 46 chromosomes, which are arranged in 23 pairs. These pairs vary in numbers and shape in different species 

Chromosomal disorder

Chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during the cell division cycle results in the gain or loss of a chromosome(s), called aneuploidy. 

Types of chromosomal disorders are Down’s syndrome, Klinefelter’s Syndrome and Turner’s Syndrome and many more.There are different types of chromosomal disorders present. Examples: down syndrome, trisomy of 18 and 13 chromosomes, Klinefelter syndrome, Turner syndrome, triple X syndrome etc. The severe type of disorder is generally caused when there is a loss and gain of chromosomes.

Most common chromosomal disorders in humans

In humans, there are several chromosomal disorders present, some of them are listed below.

Klinefelter’s Syndrome (Klinefelter, 1942)

The child suffering from this syndrome has a primary sex organ but the development of the testes is not proportionate to age. In the ill-developed interstitial cells, there is a deposition of adipose tissue. The hairs and appearance are like a female.

Development of mammary glands takes place to a lesser extent.

The man becomes sterile due to insufficient androgen levels in the blood.Genetical characteristic of Klinefelter’s syndrome: The cells of people suffering from Klinefelter’s syndrome are with 47 chromosomes as compared to the normal number of chromosomes.

This takes place due to the combination of A + XX ovum and A + Y sperm. So the zygote contains 2A + XXY chromosomes. Here XX chromosomes suppress the effect of the Y chromosome that is responsible for the expression of male characteristics.

In this way, males with feminine characters develop.

Turner’s Syndrome (Turner et al, 1938)

The frequency of this syndrome is one in every three thousand females. 

Phenotypically such individuals are female. There is an absence of adult characters and their frictions. Such female is dwarf, mentally retarded and with improper development of mammary glands. Ovaries are mostly filled with connective tissue and very deficient secretion of the estrogenic hormone. This syndrome is also called gonadal dysgenesis.

Down’s Syndrome (Mongolian Idiocy)

This trisomy affects the course of development of the individual and causes down syndrome.

Down syndrome was discovered by Langdon down in 1866 and after the discovery of down syndrome, he earned the title ‘father of syndrome’. Down syndrome varies from one individual to another and is responsible for lifetime disability and developmental delay in individuals. 

Down syndrome is also responsible for medical abnormalities like heart disease. Down syndrome is mainly known as a human chromosomal disorder.This is due to the trisomy of chromosome 21 and the total number of chromosomes is 47.

Symptoms: Average age ranges between 13-18 years, face mongoloid, short stature, underdeveloped brain, etc.

Edward’s Syndrome

This is due to trisomy of chromosome 18, survival of the individual is up to 6 months. Abnormalities are anomalies of fingers, complex digital prints, heart defects, low sets ears and smallmouth.

Patau’s Syndrome

This is due to trisomy of chromosome 13, death of the individual occurs before three months of age. Abnormalities are mental retardation, defective eyes as wel1 as heart defects, harelip, and cleft palate.

Cri-du-chat Syndrome (cat’s new syndrome)

This is due to the deletion of one arm of chromosome 5.

Abnormal physical and mental development, moon-like face, small head, crying like a kitten, etc.

Myelogenous Leukaemia

Deletion of some portion of chromosome 22 brings about the loss of N-terminal sequence, changes the conformation of C-Abl protein and activates a latent oncogenic potential. The deleted chromosome 22 is called the Philadelphia chromosome (PH1).

Alzheimer’s disease

A progressive degenerative disease of the brain which is caused by the accumulation of amyloid Proteins plagues inside neurons resulting in their degeneration. This is caused by two defective alleles, one on chromosome 21 and the other on chromosome 19.

Conclusion 

Any deviation in the nuclear division can cause chromosomal disorders in organisms. The abnormalities of chromosomes cause disorders. Turner syndrome mainly occurs in females, it affects the development of females. The most common feature which occurs in females having turner syndrome is small stature, which becomes visible in females at age of.Females having turner syndrome are infertile, they have premature ovaries. Males who have Klinefelter syndrome do not have or may have facial hairs, muscle mass or body hair. Most of the males with this syndrome produce little or no sperm. Males with Klinefelter syndrome are infertile.Disorders don’t happen normally, it happens because of abnormality in the meiosis. Women’s give birth at the age of 35 or more are at high risk of having a baby with chromosomal abnormalities because at this age the error in meiosis is more likely to happen.Some drugs, medicines, alcohol, Tobacco, toxic chemicals etc. may cause chromosomal abnormalities.