Question 33

The set of chromosomes that shows an abnormality leading to a disorder is 21.

An abnormality in the set of chromosomes 21 is associated with Down syndrome, a genetic disorder characterized by developmental and intellectual delays. This disorder arises from the presence of an extra copy of chromosome 21, known as trisomy 21.

A) 18

Chromosome 18 abnormalities, such as trisomy 18 (Edwards syndrome), do lead to serious disorders; however, they are less common than those associated with chromosome 21. While trisomy 18 results in severe developmental issues and has a high mortality rate, it is not the most recognized disorder compared to Down syndrome.

B) X

The X chromosome can be associated with various genetic conditions, such as Turner syndrome (in females) and Klinefelter syndrome (in males). However, these conditions are not classified solely as abnormalities of the X chromosome in the context of this question, which focuses on specific numeric chromosomes linked to common disorders.

C) 13

Abnormalities involving chromosome 13, such as trisomy 13 (Patau syndrome), are indeed associated with serious developmental issues, including intellectual disabilities and physical abnormalities. Despite this, trisomy 13 is rarer than the abnormalities associated with chromosome 21, making it less relevant in this context.

D) 21

An abnormality in chromosome 21 is directly linked to Down syndrome, making it the most recognized chromosomal disorder. This condition significantly impacts an individual's development and is characterized by a range of physical and cognitive challenges, establishing it as the primary answer to this question.

Conclusion

The abnormality in chromosome 21 leading to Down syndrome is well-documented and widely recognized in genetic studies. While options A, C, and B refer to other chromosomal abnormalities, they do not match the prevalence and specific disorder associated with chromosome 21, solidifying it as the correct choice.