Chromosomes are threadlike structures that are the location of genetic information within a living cell nucleus. They are central component in genetic inheritance from parents to offspring. In this blog entry, we will explore the concept of chromosomes introduction and their structure going on to delve into the disorders associated with irregularities of these small but significant members of our cells.
Chromosomes — The Discovery
A discovery with chromosomes started in the late 19th century. Starting in 1879, because the cell divides, the nucleus of cells went through a series of changes; this was first noticed by the German anatomist Walther Flemming. He called these [changes] “mitosis” and spoke of the thread-like that resulted during this action as “chromosomes”
But it was not then until the early 20th century that individuals realized the importance of chromosomes. In 1902, American geneticist Walter SUTTON and German geneticist Theodor BOVERI independently put forward the "chromosome theory of inheritance." This theory explains that orgnisims execute inherit information in the form of chromosomes and how cell division reprecends these are responsible for the character of all its organs.
The Composition and Organization of Chromosomes
Chromosomes are basically composed of DNA (deoxyribonucleic acid) and proteins. DNA coils around histone proteins to form the structure of chromatin, which are then arranged into chromosomes with the help of histones inside cells.
In the cell, during division the chromatin forms visible chromosomes, which are two identical sister chromatids connected by a CONNECTION known as centromere.
Every human cell has 23 pairs or 46 chromosomes in total. The first 22 pairs, called autosomes, and the 23rd pair determines the sex of an individual. Females have two X chromosomes and males an X chromosome plus their Y chromosome.
Chromosomal Disorders
Chromosomal disorders make that our DNA fails to be arranged into stable conditions (uneven or abnormal number or structure in chromosomes). These disorders are caused by mistakes during cell division, chemicals that mess with DNA, and mutant genes you got from your parents.
A few common chromosome disorders include:
1. Down syndrome:
Downs syndrome also known as trisomy 21 is a cause of genetic abnormality because of one extra copy of Chromosome in 21. This extra genetic information disrupts the normal development of the brain/body causing intellectual and physical disability.
The parents of the affected individual are usually genetically normal.The incidence of the syndrome increases with the age of the mother, from less than 0.1% for 20-year-old mothers to 3% for those of age 45. It is believed to occur by chance, with no known behavioral activity or environmental factor that changes the probability.
Down syndrome can be identified during pregnancy by prenatal screening, followed by diagnostic testing, or after birth by direct observation and genetic testing. Since the introduction of screening, Down syndrome pregnancies are often aborted (rates varying from 50 to 85% depending on maternal age, gestational age, and maternal race/ethnicity).
2. Turner Syndrome: A result of the loss of one X chromosome in females leading to decreased height due to delayed puberty and infertility.
Typically, those affected do not develop menstrual periods or mammary glands without hormone treatment and are unable to reproduce without assistive reproductive technology. Small chi (micrognathia), loose folds of skin on the neck, slanted eyelids and prominent ears are found in Turner syndrome, though not all will show it.Heart defects, Type II diabetes, and hypothyroidism occur in the disorder more frequently than average. Most people with Turner syndrome have normal intelligence; however, many have problems with spatial visualization that may be needed in order to learn mathematics.Ptosis (droopy eyelids) and conductive hearing loss also occur more often than average.
3. Klinefelter Syndrome: A genetic condition where males are born with two or more extra copies of chromosome X, leading to being tall, late puberty and infertile.
These symptoms are often noticed only at puberty, although this is one of the most common chromosomal disorders, occurring in one to two per 1,000 live births. It is named after American endocrinologist Harry Klinefelter, who identified the condition in the 1940s, along with his colleagues at Massachusetts General Hospital.
4. Cri-du-chat Syndrome: A condition resulting from a portion of chromosome 5 being deleted which leads to a unique high-pitched cry, delayed development and intellectual disability disorder.
Its name is a French term ("cat-cry" or "call of the cat") referring to the characteristic cat-like cry of affected children. It was first described by Jérôme Lejeune in 1963. The condition affects an estimated 1 in 50,000 live births across all ethnicities and is more common in females by a 4:3 ratio.
5. Edward's Syndrome- An extra copy of chromosome 18 leads to severe intellectual disability, growth retardation and physical features such as, abnormally small head & overlapping fingers available.
Most cases of trisomy 18 occur due to problems during the formation of the reproductive cells or during early development.
Diagnosis and treatment
The diagnosis of chromosome diseases is normally performed based on physical examination, medical history and genetic testing. Genetic testing can be done through karyotyping (that is, by looking the chromosomes under microscope) or molecular testing (by analyzing the DNA sequence of a few special genes).
The treatment of chromosome disorders is dependent on particular condition and may include a mix of the following treatments:
1. Genetic counselling: Getting information and support for family of child with chromosome disorders.
2. Prenatal testing: checking for chromosome disorders during pregnancy.
3. Medications – treatment of symptoms and related illness.
4. Surgery -to correct the physical deformity or health.
5. Therapy- Consult physical, occupational and speech therapy needed for development.
Conclusion
Chromosomes are the tiny and crucial stuff of cells that hold our genetic information. The discovery of chromosomes and its molecular machinery has transformed genetics, ushering in the era when genetics could be studied at a deeper level as well diagnosed/treated genetic disorders. For chromosome disorders, that may mean big or small impacts per individual and per family, but genetic testing and treatment options that have improved over the years have shown promise of achieving better outcomes with better quality live.