Introduction
This article will find all the essential concepts related to chromosomal disorders in humans. Malfunctions or malformations cause abnormalities in the body’s system due to abnormal chromosome constitution or number. This is referred to as chromosomal disorders. This article will also help you understand the basics of chromosomal disorders and the classification of chromosomal disorders in humans to assist you in solving all your textbook questions.
Chromosomal disorders
Chromosome number refers to the precise number of chromosomes present in a species. The chromosome number stays the same in any asexually reproducing species. Chromosomes are a part of the cell which resembles a microscopic thread. They carry genetic information which is present in the form of genes. The main feature of chromosomes is their compactness. 46 chromosomes are seen in human cells, having a length of 200 nm together (1 nm = 10− 9 meter).
Generally, 46 chromosomes are arranged in humans in 23 pairs. The size and shape of these chromosomal pairs can vary but are usually the same in number. If this pattern changes, it results in chromosome abnormalities. From 23 chromosome pairs, 22 pairs are autosomes, while the 23rd pair is the sex chromosome. Autosomes are those chromosomes that do not have a role in sex determination.
If a chromosome is absent from any of the pairs, it is referred to as a state of monosomy, and when any chromosome is duplicated, it is known as trisomy. When a part of a chromosome is deleted or missing, it is known as deletion, which can lead to errors in the development of a baby. There is also a state where one part of chromosome breaks and a portion of it reattaches to another chromosome. It is called translocation. Translocation may not cause any disorders in the human body but can lead to duplication or deletion syndrome in their children.
Chromosomal Disorders in Humans Classification
Alteration of chromosomes or genes or both leads to genetic disorders. The genetic disorders can be classified as follows:
- Chromosome disorder – When the entire chromosome or one part of the chromosome is altered, it is called a chromosomal disorder
- Single gene disorder – When the DNA in one particular gene is changed, it is called single gene disorder
- Multifactorial disorders – When disorders are due to the combination of genetic alteration and environmental factors, it is referred to as multifactorial disorders
- Mitochondrial disorders – This disorder occurs due to mitochondrial dysfunction. Mitochondrial disorders are genetic, chronic, and often inherited disorders that happen as a result of mitochondria failing to generate enough energy for the body to function properly
Most Common Chromosomal Disorders
Some common chromosomal disorders are as follows:
- Down syndrome– Trisomy 21: It is caused by the presence of an extra chromosome 21 in every cell. Patients suffering from this syndrome have 47 chromosomes instead of 46. It includes birth problems, facial features and learning problems. The child also can have heart, vision, and hearing problems. The level of down syndrome, whether mild or severe, can be dependent from child to child. Symptoms of down syndrome include eyes slant upward, small ears, smallmouth, small nose, short neck, short height, loose joints, etc.
- Edwards syndrome – Trisomy 8: It includes distinctive facial features, intellectual disability, joint, cardiac, kidney, and skeletal abnormalities. Edward syndrome is caused as a result of abnormal formation of reproductive cells. Symptoms of Edward syndrome are brain malformations, high cleft or arched palate, shortened neck with skin folds, cardiac and kidney abnormalities, absent or malformed kneecap, eye abnormalities, vertebral malformations, etc.
- Patau syndrome – Trisomy 13: The Patau syndrome is caused as a result of duplicate chromosomes from chromosome 13 present in some of the body cells. Symptoms of Patau syndrome are intellectual disability, microcephaly, holoprosencephaly, meningomyelocele, polydactyly, kidney, or a heart defect
- Klinefelter’s syndrome – 47, XXY: It only affects males. The cause of Klinefelter’s syndrome is a duplicate copy of the X chromosome. Symptoms of Klinefelter syndrome are weak muscles, slow motor development, taking longer than average to sit up, crawl and walk, delay in speaking, problems at birth, etc.
- Turner syndrome – 45, X: It only affects females. Turner syndrome is caused from missing or incomplete sex chromosome in females i.e., female is born with only one X chromosome. It affects development in females such as they do not develop breasts and menstrual periods. Symptoms of Turner syndrome are short neck, low hairline at the back of the neck, low-set ears, feet and hands puffy or swollen at birth, soft nails, etc.
Conclusion
Any deviation from the normal set of chromosomes is known as a chromosomal disorder or abnormality in the body’s system. The chromosomal disorders in humans can be classified as chromosome disorder, Single gene disorder, Multifactorial disorders, and Mitochondrial disorders. Some of the most common chromosomal disorders are Down syndrome, Edwards syndrome, Patau syndrome, Klinefelter’s syndrome, and Turner syndrome. Chromosomal abnormalities may cause problems in growth or development, miscarriage, or disease. Aneuploidy is the most common chromosomal abnormality, an abnormal chromosome number due to an extra or missing chromosome.