Introduction to Chromosome Abnormalities - Problems in the Number or Structure of Human Chromosomes
Problems with chromosome number or structure can have serious implications for the individual affected.
The human body’s cells are units that tell the body how to function. Many human cells receive instructions from the genetic material stored inside, specifically, in a functioning structure called a nucleus. Inside this nucleus, the genetic materials takes the form of 46 chromosomes, structures of DNA and proteins.
DNA can also be found in other organelles called mitochondria, which are responsible for giving cells their energy. However, references to chromosomes in humans often refer only to the 46 linear chromosomes found in nuclei. These are in fact 23 pairs, one set inherited from each parent.
The genetic material stored in chromosomes is very important. Changes in the number or position of genes sometimes result in unwanted intellectual and/or physical features that are not present in those with no abnormality. There are many different types of chromosome abnormality, varying in features and severity.
Types of Chromosome Abnormalities
Errors can lead to monosomy, when a pair is missing a chromosome, or trisomy, when the pair exceeds two chromosomes. There can also be abnormalities in a chromosome’s structure, such as missing pieces or pieces breaking off and attaching to other chromosomes.
Down’s Syndrome is also called trisomy 21, as people with this disorder have an extra (or part of an extra) chromosome 21. There are different types of syndrome, for example, in some people with Down’s syndrome the abnormality in present in some cells and not all (mosaicism).
The article What is Down's syndrome? on the Down syndrome Scotland site points out that with Down’s syndrome experience learning difficulties and share some facial characteristics. People with Down’s syndrome may also have physical health issues, such as conditions of the heart, thyroid and/or muscle tone problems.
Sometimes abnormalities are inherited, or transmitted after an error in meiosis. The Philadelphia chromosome is an example of an abnormality that occurs after conception, where a part of chromosome 9 becomes attached to chromosome 22. This is a very serious error, resulting in cancer of the blood.
Detecting Chromosome Abnormalities
Scientists can take samples of a person’s cells. They then use magnification and staining techniques to make the chromosomes visible, and in turn create a karyotype. A karyotype is a picture of a person’s chromosomes, and such pictures are used to identify problems with chromosome number or structure.
Sources
Genes and chromosomes, Centre for Genetics Education http://www.genetics.edu.au/publications-and-resources/facts-sheets/fact-sheet-1-an-introduction-to-dna-genes-and-chromosomes/view
Chromosome Abnormalities, National Human Genome Research Institute https://www.genome.gov/11508982/chromosome-abnormalities-fact-sheet/
How do scientists read chromosomes?, Genetic Science Learning Center http://learn.genetics.utah.edu/content/basics/readchromosomes/
Down syndrome Scotland https://www.dsscotland.org.uk/
Fascinating post, thank you. I did not know down syndrome was from having extra chromosome. Will check back for more. thanks again.
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