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Karyotyping is perfomed in the field of cytogenetics for many reasons. If amniocentesis is performed on a woman, the sex of the child can be determined by observing the XX (female) or XY(male) chromosome pair. Another purpose is to look for aneuploidy. Aneuploidy is when the chromosome number within a species varies from the "norm" being the diploid or 2n condition. For example, monosomy (2n-1)can be observed if a person's karyotype is missing one of the X chromosomes. This condition is called Turner's Syndrome. Another example of aneuploidy is trisomy(2n+1). In this case, an individual has three chromosomes rather than the normal pair at a particular location. Down's Syndrome is also known as trisomy 21, because an additional chromosome is located at the 21st pair. It is generally due to the age of the mother. After 35, the number of Down's Syndrome births significantly increases. Another example of trisomy is Klinefelter's syndrome. In this case, an individual has an extra sex chromosome and is XXY. Sometimes, a karyotype can show additional sets of chromosomes like the triploid condition, where the individual has three sets of chromosomes, rather than two. Ploidy is more common in the plant kingdom but can occur in animals. Sometimes, a chromosome can be missing a piece or have extra chromosome material. An example of a disorder caused by missing part of chromosome 5 is Cri du Chat syndrome. Angelmann syndrome is due to a missing part of chromosome 15.
Karyotyping is important when people want to find out if their children will have any genetic disorders that involve trisomy or monosomy.
In trisomy, an individual has an EXTRA chromosome. This can result in mental retardation, disorders, and even shortened life expectancy. An example is trisomy 21. You may know this more commonly as Down Syndrome. When someone has down syndrome, they have an extra chromosome number 21. By the way, trisomy means 3 chromosomes ("tri" means three).
In monosomy, an individual has one LESS chromosome. An example is called Turner's syndrome. This is when an offspring has only one sex chromosome,, and their genotype is X0 for gender.
When parents are interested or nervous about whether or not their unborn baby will have a genetic disorder, they can have a doctor prepare a karyotype of the unborn child. Then they can decide what they want to do about any negative feedback they get
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