Zoology - Principles of Inheritance and Variation Question with Solution | TestHub

Down's syndrome is due to an extra chromosome number$21.$The patient's cells have 3 copies of 21st chromosome (Trisomy 21) instead of homologous pair. It occurs due to failure of separation of homologous chromosomes or non-disjunction during meiosis (gamete formation). Symptoms of Down's syndrome:

$\left(\mathrm{a}\right)$Patients show Mental retardation

$\left(\mathrm{b}\right)$Due to poor skeletal development, they have short stature and relatively small skull

$\left(\mathrm{c}\right)$Their face is typically flat with rounded flat nose

$\left(\mathrm{d}\right)$They have an open mouth, protruding tongue and a high arched palate.

$\left(\mathrm{e}\right)$Most children show typical facial features with a fold of skin (epicanthal skin fold) over the inner corner of the eye. This results in downward slanting of eyelids.

$\left(\mathrm{f}\right)$They have flat hand with characteristic crease which runs all the way across the palm (Simian crease).