Question

Down’s syndrome is due to
A. Non-disjunctions of chromosomes
B. Crossing over between genes
C. Linkage of genes
D. Sex-linked inheritance

Answer 1

Hint: It is a disorder that is associated with meiosis stage of the cell division process. It is caused due to improper separation of the genetic material during the anaphase stage.

Complete answer:
Down syndrome is a genetic condition induced by an additional full or partial copy of the 21st chromosome resulting in irregular cell division. Itranges among individuals in seriousness, causing lifelong intellectual impairment and delay in growth. It is the most prevalent hereditary chromosomal problem in children. Other clinical anomalies include cardiac and gastrointestinal problems. During maternal meiosis I, nondisjunction happens in the majority of cases. In at least 0.3% of newborn babies, trisomy occurs and in 25% of spontaneous abortions. It is the significant cause of waste in labour and the most prevalent cause of cognitive impairment. It is well stated that an increased risk of meiotic nondisjunction leading to the down syndrome is linked with advanced maternal age. It can be related to the persistent meiotic arrest of human oocytes which can last for more than four decades.
So, the correct answer is option is A.

Additional information: Today, based on the severity of medical conditions, everyone with down syndrome could expect to live more than 60 years. The procedure involves the pre-implantation genetic diagnosis which is beneficial for couples who seem to have a family background of genetic disorders. Use of stem cells and gene therapy are other two other efforts under investigation.

Note: Symptoms of the down syndrome include: flattened face, protruding tongue, upward slanting eyelids, fairly short fingers, short height, etc. The use of antioxidants, gamma-secretase reduction, adrenergic agonists and memantine are some other approaches that are now being examined. Testing is also conducted on experimental animals, such as the mouse Ts65Dn.