First, we have the numerical abnormalities. It occurs when an individual is missing one of the chromosomes from a pair. That condition is called monosomy. When an individual has more than two copies instead of a pair, the conditions is called trisomy, an example, of a condition caused by numerical abnormalities is Down’s syndrome which is marked by some mental disability, we could have learning difficulties, a characteristic facial appearance, they could have a poor muscular tone but an individual with dysentery has three copies of chromosome 21 rather than two for that the reason this condition is also known as trisomy 21. An example of monosomy in which an individual lacks a chromosome is Turner’s syndrome. In Turner’s syndrome, a female is born with only one sex chromosome X, it is number to have instead of for example find a female uh two X chromosome, the sexual chromosomes and instead of boys one X chromosome and one Y chromosome but in this case in Turner’s syndrome, they only have one sex chromosome and it’s usually shorter than average unable to have children, for example, among other difficulties and as we have mentioned we have a structural abnormalities. This this is a chromosome structure that can be altered in several ways, we could mutations, alterations, portion of the chromosome is missing, duplications when a portion is duplicated, translocation when a portion of the one chromosome is transferred to another chromosomes and this could lead in, for example, two miscarriages – this is very rare because it is just less than five percent of the population so, that is very important to assess our patients when they get here to the lab or to the clinic, to handle and to assess the risk that they could have. We could have inversions and last but not least rinse that is a portion of a chromosome that has broken off and form a circle or ring. These happen with or without loss of genetic material so, it is important to sum up that most chromosome abnormalities occur as an accident in an egg or a sperm. In these cases that abnormality is present in every cell of the body. Some of the abnormalities however happen after conception, then some cells have abnormalities and some do not but it is important that chromosomal abnormalities can be inherited from a parent such a translocation in this case that we could have and this is the most common to be the noble. What means noble – the number that is new to the individual and it happens for the first time in this individual and they didn’t inherit this from their parents so, this is why when a child is found to have another abnormality, chromosomal studies and offers are performed on the parents.
Examples given before are large deletions and inversions involving millions of letters of DNA that may or may not be picked up by karyotyping. It’s very unlikely that karyotyping will pick up any very large changes. There are also large duplications of DNA letters or full chromosomes, and Kleinfelder has got an extra X chromosome, as I mentioned earlier. Unfortunately, having too many X chromosomes causes infertile syndrome and other problems. There are also rare chromosomal swapping events where one part of one particular chromosome, for example, chromosome one, swaps with someone’s DNA with another chromosome, chromosome two. This is known as the Balance Translocation Event. Some of these events are associated with recurrent pregnancy loss when swapping two letters to different chromosomes.
