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Trisomy 21: association between reduced recombination and nondisjunction
S L Sherman1, N Takaesu, S B Freeman
1Department of Pediatrics, Emory University School of Medicine, Atlanta, GA 30322.
American Journal of Human Genetics
|September 1, 1991
Summary
Recombination and nondisjunction of chromosome 21 were studied using DNA markers. Reduced recombination in mothers significantly increases the risk of trisomy 21 (Down syndrome).
Area of Science:
- Genetics
- Molecular Biology
- Human Chromosomes
Background:
- Nondisjunction of chromosome 21 is the primary cause of trisomy 21 (Down syndrome).
- The role of recombination in chromosome 21 nondisjunction is not fully understood.
- Previous cytogenetic studies suggest a high maternal nondisjunction rate.
Purpose of the Study:
- To investigate the association between genetic recombination and nondisjunction of chromosome 21.
- To determine the parental origin of nondisjunction events in trisomy 21.
- To develop a genetic map of chromosome 21 to assess recombination patterns.
Main Methods:
- Analysis of cytogenetic and DNA markers in 104 individuals with trisomy 21 and their parents.
- Determining parental origin of nondisjunction using informative DNA markers.
- Construction of a genetic map of chromosome 21 using maternally derived cases.
Main Results:
- Maternal origin of nondisjunction was confirmed in 94% of informative cases, exceeding typical rates.
- A genetic map of chromosome 21's long arm was created.
- The genetic map was significantly shorter than the normal female linkage map, indicating reduced recombination.
Conclusions:
- Absence or reduction of pairing and recombination significantly contributes to nondisjunction in a substantial proportion of trisomy 21 cases.
- Molecular approaches offer increased accuracy in determining nondisjunction rates and origins.
- Findings highlight the critical role of recombination in preventing chromosome 21 nondisjunction.