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In a trisomy, one or parts of one chromosome is present in three copies instead of two copies. In humans, a trisomy of chromosome 21, known as Down's syndrome, is common and occurs with an increased age of the mother at the time of conception Connection.
Children with a trisomy of chromosomes 13 or 18 are also viable, but usually die very early. Trisomies of all other autosomal chromosomes are fatal for the embryo.
Of the Karyotype In cytogenetics denotes the entirety of all cytologically recognizable chromosome properties of an individual or a group of genetically related individuals. These properties include the number of chromosomes in a cell as well as their formation, their relative and absolute size, the position of the centromere, secondary constrictions, specific banding patterns and the distribution of chromatin in the chromosome.
The karyotype is determined by chromosomes in the metaphase of mitosis made recognizable by chromosome staining and examined with a light microscope. For human genetic diagnostics, it has proven useful to photograph the chromosomes and then arrange them in pairs to form a karyogram.