Chromosomal Disorders and Abnormalities — NEET Biology

Correct answer: B — S1, S2 and S4 only

The statements that are NOT correct are S1, S2, and S4. S1 is NOT correct: Chromosomal disorders are caused due to absence, excess or abnormal arrangement of one or more chromosomes, not typically by alteration or mutation in a single gene. Alterations in a single gene characterise Mendelian disorders. S2 is NOT correct: Aneuploidy refers to the gain or loss of a chromosome(s). The increase in a whole set of chromosomes is known as polyploidy, which is often seen in plants. S3 is correct: Down's syndrome is caused by the presence of an additional copy of chromosome 21 (trisomy of 21), leading to characteristic features including mental retardation. S4 is NOT correct: Individuals with Klinefelter's syndrome (karyotype 47, XXY) exhibit overall masculine development but also feminine development (gynaecomastia) and are sterile. They do not have rudimentary ovaries; rudimentary ovaries are characteristic of Turner's syndrome. S5 is correct: Turner's syndrome is caused by the absence of one of the X chromosomes, resulting in a karyotype of 45, X0, leading to sterile females with rudimentary ovaries. Therefore, statements S1, S2, and S4 are NOT correct. This question tests the understanding of definitions, causes, and specific karyotypes and symptoms of chromosomal disorders.