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Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with developmental delays, mild to moderate intellectual disability, and characteristic physical features.
Turner syndrome ( TS ), also known as 45,X, or 45,X0, is a genetic disorder in which a person's cells have only one X chromosome or are partially missing an X chromosome ( sex chromosome monosomy ). [2] [6] Most people have two sex chromosomes (XX or XY).
Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on chromosome 21, 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 ...
Frequency. ~1 in 1,000 males [1] XYY syndrome, also known as Jacobs syndrome, is an aneuploid genetic condition in which a male has an extra Y chromosome. [1] There are usually few symptoms. [2] These may include being taller than average and an increased risk of learning disabilities.
XXYY syndrome is a sex chromosome anomaly in which males have 2 extra chromosomes, one X and one Y chromosome. Human cells usually contain two sex chromosomes, one from the mother and one from the father. Usually, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The appearance of at least one Y chromosome with ...
World Down Syndrome Day (WDSD) is marked each year on March 21, beginning in 2007. The 21st day of March (the 3rd month of the year) was selected to signify the uniqueness of the triplication ( trisomy ) of the 21st chromosome which causes Down syndrome .
XXXY syndrome is a genetic condition characterized by a sex chromosome aneuploidy, where individuals have two extra X chromosomes. [2] People in most cases have two sex chromosomes: an X and a Y or two X chromosomes. The presence of one Y chromosome with a functioning SRY gene causes the expression of genes that determine maleness.
A mother's age is one of the many environmental factors that might lead to genetic abnormalities. The implications of chromosomal abnormalities depend on the specific problem, they may have quite different ramifications. Some examples are Down syndrome and Turner syndrome.
In a small percentage of cases, Down syndrome is caused by a rearrangement of chromosomal material between chromosome 21 and another chromosome. As a result, a person has the usual two copies of chromosome 21, plus extra material from chromosome 21 attached to another chromosome.
Recent research has identified a region of the chromosome that contains the main genes responsible for the pathogenesis of Down syndrome, located proximal to 21q22.3. The search for major genes involved in Down syndrome characteristics is normally in the region 21q21–21q22.3.