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  4. A woman with 47 chromosomes due to three copies of chromosome 21 is characterized by

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Q. A woman with 47 chromosomes due to three copies of chromosome 21 is characterized by

AIPMTAIPMT 2005Principles of Inheritance and Variation

Solution:

Down's syndrome is caused by the presence of an extra chromosome number 21. Both the chromosomes of the pair 21 pass into a single egg. Thus, the egg possesses 24 chromosomes instead of 23 and offspring has 47 chromosomes (45 + XY in males, 45 + XX in males) insted of 46. Turner's syndrome is formed by the union of an abnormal O egg and a normal X sperm or a normal egg and an abnormal O sperm. The individual has 45 chromosomes (44 + X) instead of 46. Female with more than two X chromosomes is called superfemale. Triploidy is a condition in which an organism has three times (3n) the haploid number (n) of chromosomes.