HEREDITY
NONDISJUNCTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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21
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23
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45
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46
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47
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Detailed explanation-1: -In about 95% of cases, there is an extra separate chromosome 21 (trisomy 21), which is typically maternally derived. Such people have 47 chromosomes instead of the normal 46. Down syndrome is characterized by an extra chromosome 21 (see arrow).
Detailed explanation-2: -Also known as Down syndrome, trisomy 21 is a genetic condition caused by an extra chromosome. Most babies inherit 23 chromosomes from each parent, for a total of 46 chromosomes. Babies with Down syndrome however, end up with three chromosomes at position 21, instead of the usual pair.
Detailed explanation-3: -Instead of the usual 46 chromosomes present in each cell, Lejeune observed 47 in the cells of individuals with Down syndrome.
Detailed explanation-4: -Down syndrome karyotype (formerly called trisomy 21 syndrome or mongolism), human male, 47, XY, +21. This male has a full chromosome complement plus an extra chromosome 21.
Detailed explanation-5: -There is a full set of 23 homologous pairs of autosomes, and an X and Y, but an extra chromosome 21. These individuals are also said to have Down syndrome.