Genetic Origins of Down Syndrome

Genetic Origins Of Down Syndrome

Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 21st chromosome, either in whole (trisomy 21) or part (such as due to translocations). The effects of the extra copy varies greatly from individual to individual, depending on the extent of the extra copy, genetic background, environmental factors, and random chance. Down syndrome can occur in all human populations, and analogous effects have been found in other species, such as chimpanzees and mice. Recently, researchers have been able to create transgenic mice with most of human chromosome 21 (in addition to their normal chromosomes).

A normal human karyotype is shown here. Every chromosome has two copies. In the bottom right, there are chromosomal differences between males (XY) and females (XX), which do not concern us. A normal human karyotype is designated as 46,XX or 46,XY, indicating 46 chromosomes with an XX arrangement for females and 46 chromosomes with an XY arrangement for males. For this section, we will use females for the karyotype designation (46,XX).

The extra chromosomal material can come about in several distinct ways. These are explained in the following sections.

Read more about Genetic Origins Of Down Syndrome:  Trisomy 21, Translocation Down Syndrome, Mosaicism, Duplication of A Portion of Chromosome 21

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Genetic Origins Of Down Syndrome - Duplication of A Portion of Chromosome 21
... If the duplicated region has genes that are responsible for Down syndrome physical and mental characteristics, such individuals will show those characteristics ...

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