Humans have 46 chromosomes in 23 pairs that vary in size and shape and are numbered in accordance with convention. Twenty-two of the pairs are autosomes, whereas one is a pair of sex chromosomes (number 23). Any divergence from this pattern results in abnormalities. A chromosome can be duplicated (trisomy) or missing (monosomy); an entire set of 23 chromosome pairs can be duplicated three times (triploidy) or more (polyploidy); or one arm or part of one arm of a single chromosome can be missing (monosomy) (deletion). A fragment of one chromosome can be transferred to another (translocation), which has no effect on the individual but frequently results in a deletion or duplication syndrome in his or her offspring.
Changes in chromosome number occur during the formation of sperm or eggs, as well as during the embryo’s early development. In the latter case, mosaicism might occur, which is defined by a mix of cells, some of which are normal (euploid) and others that have abnormal chromosome complements. In either case, the chromosomes’ distinct genetic signals cause developmental abnormalities. One of these chromosomal abnormalities occurs in 0.5 percent of all births.
Types of Chromosomal abnormalities:
Down syndrome (previously known as mongolism), a chromosome 21 trisomy, was the first detected chromosomal anomaly (in 1959); it is the most common trisomy and the major cause of intellectual disability. Intellectual impairment is the most common manifestation of chromosomal abnormalities, and it occurs in some form in all substantial autosomal abnormalities. Several chromosomal diseases, including Down syndrome, have been linked to heart disease and malformations. Atypical sexual development, behavioural issues, cancer (for example, the Philadelphia chromosome in chronic myelocytic leukaemia), and spontaneous abortion are all symptoms of chromosomal anomalies. Because sex chromosomal abnormalities are more common than autosomal abnormalities, they have less severe implications. Turner’s syndrome (XO), Klinefelter’s illness (XXY), and the so-called “supermale” are all caused by sex chromosomal distribution irregularities (XYY). Turner’s and Klinefelter’s syndromes are characterised by female and male genitalia, respectively, as well as delayed sexual development. Supermales are typically taller than average and have learning disabilities. Although some studies have suggested a link between supermaleness and criminal behaviour, the theory has been widely rejected. In reality, many XYY people are socially well-adjusted.
Humans have forty-six chromosomes organised in twenty-three pairs. A slight divergence from this pattern, on the other hand, results in anomalies. Chromosome disorders are caused by changes in chromosomal number or chromosomal structure. Nondisjunction of chromosomes, or the failure of chromatids to disjoin during cell division, results in chromosomal number variations, which can be aneuploidy or euploidy. Aneuploidy is a condition in which one or more chromosomes either gain or lose function. Aneuploidy is classified into two types: trisomy and monosomy. In a diploid person, there are 2n chromosomes. Trisomy is a condition in which an extra chromosome is introduced. Monosomy, on the other hand, happens when a chromosome is partially or completely lacking.
Euploidy is a polyploidy state characterised by the failure of cytokinesis, resulting in the development of more than two haploid sets of chromosomes. Depending on the number of chromosomal sets added, euploidy can be triploidy, tetraploidy, pentaploidy, and so on.
Down’s Syndrome is caused by the existence of an extra copy of the twenty-first chromosome.
A swollen face, bulging and slanting eyes, a small mouth, and a protruding and wrinkled tongue are all signs.
Males with Klinefelter’s Syndrome are born with an additional X-chromosome, resulting in a karyotype of 47, or XXY. Some of the most common sex chromosomal issues in males are poor beard growth, narrow shoulders, gynaecomastia or breast development, and underdeveloped testis. Moreover, those men are sterile.
Turner’s Syndrome is a syndrome in which one of the female X-chromosomes is missing. These females will have 45 chromosomes, including the XO chromosome. A webbed neck, aortic constriction, poor breast development, undeveloped ovaries, and diminutive stature in females are all symptoms of this illness.
Conclusion:
Chromosome structural alterations might manifest themselves in a variety of ways. As part of these adjustments, a chromosomal fragment may be deleted, duplicated, or moved to another chromosome. While some of these chromosome structural changes are inherited, others occur by chance during the formation of reproductive cells or during early fetal development. Illnesses such as Jacobsen Syndrome and Cri-du Chat Syndrome are caused by changes in chromosomal structure. As a result, chromosomes hold the genetic keys to all of our body’s actions, and any change in chromosome number or structure might cause chromosomal disorders.