Numerical & Structural Aberrations | Anthropology Optional for UPSC PDF Download

Introduction

• Our bodies contain 46 chromosomes, arranged in 23 pairs, which we inherit from our parents—half from the mother and the other half from the father. As previously studied, females typically have two X chromosomes, while males have one X and one Y chromosome in each body cell. These chromosomes carry the essential instructions for our bodies to grow and develop properly.
• Chromosomal disorders, which are a type of genetic disorder, occur when there is a change in the number or structure of the chromosomes inherited from our parents. These disorders typically arise during the development of the fetus or from the moment of conception. Chromosomal disorders can be primarily categorized into two types: numerical and structural.

Numerical aberration

Numerical aberrations in chromosomes refer to the presence of an incorrect number of chromosomes in a cell, either less than 46 or more than 46. There are two main types of numerical aberrations: monosomies and trisomies.

• Monosomies occur when there is only one copy of a chromosome instead of the expected two copies in diploid cells. This results in a total of 45 chromosomes instead of the normal 46. Monosomies are rare in humans, and in most cases, the unborn child doesn't survive due to the missing chromosome. Turner syndrome is a common disorder caused by this abnormality, affecting girls and causing developmental problems, such as shorter stature, delayed puberty, and health issues related to kidneys and heart.
• Trisomies, on the other hand, happen when there is an extra copy of a chromosome, leading to a total of 47 chromosomes instead of 46. Some common disorders caused by trisomies include Down syndrome, Edward syndrome, and Patau syndrome. Down syndrome, for example, has three types, with the most common being Standard Trisomy 21. This occurs when an extra chromosome is present in either the mother's egg or the father's sperm. Individuals with Down syndrome often experience developmental delays and learning difficulties.

Structural Aberrations

 Structural aberration refers to alterations in the structure of a chromosome, which can occur at any time, such as during the formation of egg cells in females, sperm cells in males, or even during fetal development. Some structural disorders may lead to health problems, while others may not have significant health consequences. Structural aberrations can be classified into four sub-categories:

• Deletion: This type of mutation involves a deficiency in the chromosome or DNA sequence, where a portion is missing or deleted during DNA replication. The deletion can range from a single base to an entire section of the chromosome. Large deletions can be fatal, as they may result in the loss of essential genes.
• Duplication: In this case, a chromosomal segment is duplicated, resulting in two copies of the segment being present in the original location on the chromosome. This leads to extra genetic material, even though the overall number of chromosomes remains normal. Since a chromosome contains multiple genes, the duplication or presence of an extra gene can cause dysfunction in those genes. As a result, the additional gene may lead to improper development of the baby due to the presence of "extra instructions."
• Inversion: In the context of structural abnormalities in chromosomes, inversion refers to the process where a segment of a chromosome is reversed end-to-end. This occurs when a chromosome experiences breakage, followed by a rearrangement within the chromosome itself. Inversions can be classified into two categories: pericentric and paracentric. In pericentric inversions, the breakage point occurs in each arm of the chromosome, involving the centromere. On the other hand, paracentric inversions involve breakage in the chromosome arms, but the centromere is not included. Generally, inversions do not result in abnormalities as long as the rearrangement remains balanced, with no extra or missing DNA. However, in heterozygous individuals, there is a higher likelihood of producing abnormal chromatids.
• Translocation: The term translocation refers to the change in location, specifically in the context of genetics, where a part of a chromosome is transferred to another chromosome. Since chromosomes carry genes, which are the hereditary units, translocation can lead to issues within the chromosomes. In this type of abnormality, a chromosome breaks and a portion of it attaches to a different chromosome. This process of translocation can increase the risk of developing diseases such as leukemia, breast cancer, and Down syndrome.

Conclusion

Chromosomal disorders are genetic disorders that occur due to changes in the number or structure of chromosomes inherited from our parents. These disorders can be categorized into numerical and structural aberrations. Numerical aberrations involve an incorrect number of chromosomes, leading to monosomies or trisomies, while structural aberrations involve alterations in the structure of chromosomes, leading to deletion, duplication, inversion, or translocation. These abnormalities can result in various health issues, developmental delays, and even death in some cases. Understanding and identifying these chromosomal disorders can help in early diagnosis and management of the associated health risks.