Physical,psychomotor,and mental development is retarded in an individual affected with

In humans,which disorder is caused due to the absence of one of the $X$ chromosomes,i.e.,$45$ with $XO$?

Choose the correct answer regarding the following statements:
$(i)$ Sickle-cell anaemia is controlled by three pairs of alleles.
$(ii)$ Trisomy is a chromosomal disorder.
$(iii)$ $47$ chromosomes are present in a person having Turner's syndrome.

In which one of the following combinations $(a - d)$ the number of chromosomes of the present-day hexaploid wheat is correctly represented?

The $Cri-du-chat$ syndrome is caused by a chromosomal structural change involving:

Explain the difference between Euploidy and Aneuploidy.