What are chromosome abnormalities and how often do they occur?
Each of our chromosomes has a specific and proper structure and colour. Together, they form a distinct pattern called the human karyotype. We have 46 chromosomes (23 from each parent). But biology being biology, there are variations in reproduction resulting in abnormalities in the karyotype of an individual. A very few are beneficial, most are harmless, a few are catastrophic. A major chromosome abnormality (MCA) accounts for half of all spontaneous human abortions. A MCA occurs in about one in every 100 to 200 births. Recent medical diagnostic techniques can now detect many MCAs long before the child is born. They do this by analysing the patient’s blood under a microscope. MCAs take one of five forms. • In duplication, instead of the normal two, the individual has three copies of the chromosome in every cell of their body (trisomic). Most trisomics result in a spontaneous abortion – but not always. Trisomy-21 (Down’s Syndrome) occurs 1.5 times in every 1,000 births. The individual h
Asked by Lynn Davis of Casper, Wyoming Each of our chromosomes has a specific and proper structure and colour. Together, they form a distinct pattern called the human karyotype. We have 46 chromosomes (23 from each parent). But biology being biology, there are variations in reproduction resulting in abnormalities in the karyotype of an individual. A very few are beneficial, most are harmless, a few are catastrophic. A major chromosome abnormality (MCA) accounts for half of all spontaneous human abortions. A MCA occurs in about one in every 100 to 200 births. Recent medical diagnostic techniques can now detect many MCAs long before the child is born. They do this by analysing the patient’s blood under a microscope. MCAs take one of five forms. • In duplication, instead of the normal two, the individual has three copies of the chromosome in every cell of their body (trisomic). Most trisomics result in a spontaneous abortion – but not always. Trisomy-21 (Down’s Syndrome) occurs 1.5 times
