Question

Which of the following is not caused by a single non-disjunction?

• A. Spontaneous miscarriage of the fetus
• B. 47 chromosomes per somatic cell
• C. 45 chromosomes per somatic cell
• D. Congenital disorders such as Down syndrome
• E. Breakage near the centromere

Answer 1

The correct option is E Breakage near the centromere

Single non-disjunction refers to the imperfect separation of homologous chromosomes or sister chromatids during cell division. This scenario is classified on basis of the stage at which the incomplete separation takes place i.e at meiosis-I, meiosis-II or mitosis.

The impact of this phenomena includes sudden miscarriage, aneuploidy (abnormal number of chromosomes in daughter cells: monosomy, euploidy, 45 XX, 47 XXX or XXY, etc) and co-genital disorder like Klinefelter syndrome, Edward's syndrome, Down's syndrome, etc.

Hence, the correct answer is 'Breakage near the entrance'.