Principles of Inheritance and Variation Question 209

209. Down’s syndrome is due to

[1992]

(a) crossing over

(b) linkage

(c) sex-linked inheritance

(d) nondisjunction of chromosomes

Show Answer

Answer : d

Hints & Solution

(d) Down’s syndrome is due to nondisjunction of chromosomes. Non-disjunction means absence of separation of two homologous $X$ chromosomes during anaphase-I of meiosis. Both $X$ chromosomes go together to same pole. Other pole will receive no $X$ chromosome.