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Trisomy 21. Down syndrome (also known by the karyotype 47,XX,+21 for females and 47,XY,+21 for males) [98] is mostly caused by a failure of the 21st chromosome to separate during egg or sperm development, known as nondisjunction. [91] As a result, a sperm or egg cell is produced with an extra copy of chromosome 21; this cell thus has 24 ...
Genetics of Down syndrome. 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 ...
Down syndrome is a genetic disorder that often results in distinct physical differences and intellectual disability. According to the Centers for Disease Control, each year about 6,000 babies are ...
The average IQ of a young adult with Down syndrome is 50, equivalent to the mental age of an 8- or 9-year-old child, but this number varies widely. [3] At the same time, they enjoy a rich social and emotional awareness. [4] Down syndrome is the most common chromosome abnormality in humans, [3] occurring in about one per 1000 babies born each ...
Robertsonian translocation (ROB) is a chromosomal abnormality where the entire long arms of two different chromosomes become fused to each other. It is the most common form of chromosomal translocation in humans, affecting 1 out of every 1,000 babies born. [1] It does not usually cause medical problems, though some people may produce gametes ...
Down syndrome research. Research of Down syndrome–related genes is based on studying the genes located on chromosome 21. In general, this leads to an overexpression of the genes. [1][2] Understanding the genes involved may help to target medical treatment to individuals with Down syndrome. It is estimated that chromosome 21 contains 200 to ...
John Langdon Down. John Langdon Haydon Down (18 November 1828 – 7 October 1896) was a British physician best known for his description of the genetic condition now known as Down syndrome, which he originally classified in 1862. He is also noted for his work in social medicine and as a pioneer in the care of mentally disabled patients.
Research has found that there is a correlation between advanced paternal age and risk of birth defects such as limb anomalies, syndromes involving multiple systems, and Down syndrome. [74] [35] [93] Recent studies have concluded that 5-9% of Down syndrome cases are due to paternal effects, but these findings are controversial. [74] [75] [35] [94]