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Trisomy


trisomy
the diploid condition plus one extra chromosome: 2n + 1
Source: Jenkins, John B. 1990. Human Genetics, 2nd Edition. New York: Harper & Row ...
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Dr. Leslie Biesecker, of the National Human Genome Research Institute's Laboratory of Genetic Disease Research, defines trisomy.
illustrated:
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Trisomy 21 (47,XX,+21) is caused by a meiotic nondisjunction event. A normal egg has one copy of each chromosome (23 total). When it is combined with a sperm from the other parent during conception, the child has 46 chromosomes.
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Trisomy 18 is therefore caused by a genetic abnormality occurring before conception, when egg and sperm cells are made.
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Trisomy
The term proposed by Blakeslee (1922) to describe an otherwise diploid individual which has one of the chromosomes represented three times instead of twice. Caused by nondisjunction during cell division.
Related Terms: Diploid ...
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Trisomy 18 (Edward Syndrome)
Trisomy 18 is associated with mental and physical retardation, skull and facial abnormalities, defects in all organ systems, and poor muscle tone.
Mean survival is 2 to 4 months.
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trisomy A condition where a cell has an extra chromosome.
trophoblast The outer layer of cells of a blastocyst that adhere to the endometrium during implantation.
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Trisomy Possessing three copies of a particular chromosome instead of the normal two copies.
See also: cell, gene, gene expression, chromosome
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Advanced maternal age -- women over age 34 (age 35 at delivery) at increased risk for nondisjunction trisomy in fetus. Alcoholism -- a chronic and progressive condition characterized by the inability to control the consumption of alcohol.
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Three of the same chromosome ("trisomy") is also lethal except for chromosomes 13, 18, and 21 (trisomy 21 is the cause of Down syndrome).
Three or more X chromosomes are viable because all but one of them are inactivated. [Link to discussion] ...
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nondisjunction. Failure of a pair of homologous chromosomes to separate during meiosis, leading to one gamete with n + 1 chromosomes (see trisomy) and another gamete with n _ 1 chromosomes.
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uniparental disomy
, it may cause
trisomy 21
(Down's syndrome) in the offspring. Human chromosome 2 is a result of a centric fusion between two ancestral ape chromosomes (gorillas have 24 pairs of chromosomes).
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