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Question
Down syndrome and Turner syndrome are due to respectively
Down syndrome and Turner syndrome are due to respectively
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Solution
The correct option is D Trisomic and monosomic conditions
The presence of one chromosome in triplicate (2n+1) is called as trisomy. The presence of full or partial extra three copies of chromosome 21 causes Down syndrome. Thus, it is trisomy 21 and is represented as 45 + XY or 45 + XX. The absence of one X-chromosome causes Turner's syndrome which is represented as 44 + XO. Monosomy is the absence of a single chromosome from a diploid cell (2n-1); thus Turner syndrome is a monosomy. Nullisomy is the absence of one complete pair of homologous chromosomes (2n-2) which makes options A and D wrong as in both disorders, the complete pair is not missing. The presence of one chromosome four times is called as tetrasomy (2n+2) which makes options C and D wrong. The correct answer is B.
The presence of one chromosome in triplicate (2n+1) is called as trisomy. The presence of full or partial extra three copies of chromosome 21 causes Down syndrome. Thus, it is trisomy 21 and is represented as 45 + XY or 45 + XX. The absence of one X-chromosome causes Turner's syndrome which is represented as 44 + XO. Monosomy is the absence of a single chromosome from a diploid cell (2n-1); thus Turner syndrome is a monosomy. Nullisomy is the absence of one complete pair of homologous chromosomes (2n-2) which makes options A and D wrong as in both disorders, the complete pair is not missing. The presence of one chromosome four times is called as tetrasomy (2n+2) which makes options C and D wrong. The correct answer is B.
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