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Q.
The chromosomal condition of Down's syndrome is?
COMEDKCOMEDK 2012Principles of Inheritance and Variation
Solution:
Down's syndrome is the trisomy of 21 st chromosome (autosomal aneuploidy) in man. Down's syndrome is characterized by short stature, warty skin, protruding tongue, slanting eyes, with folded eyelids (epicanthus folds), short, broad hands with palmer crease, fingers showing characteristic fingerprint patterns. The affected person's face presents a typical mongoloid look. Hence it is also called as mongoloid idiocy. It occurs due to the phenomenon of non-disjunction. Noh-disjunction occurs when a pair of homologous chromosomes does not separate in meiosis but migrate to the same pole of the cell resulting in an uneven number of chromosomes in the daughter cells (47 in one and 45 in other). This numerical abnormality results in trisomy, (2n + 1) and monosomy (2n- 1) respectively. Non-disjunction is more common in sex chromosomes.