Based on Lyon's hypothesis,what will be the number of Barr bodies found in a human female suffering from Down's syndrome?

In which of the following disorders does an affected individual possess $47$ chromosomes?

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.

Gynecomastia is a symptom of

Which of the following statements are correct about Klinefelter's Syndrome?
$A$. This disorder was first described by Langdon Down $(1866)$.
$B$. Such an individual has overall masculine development. However,the feminine development is also expressed.
$C$. The affected individual is short statured.
$D$. Physical,psychomotor and mental development is retarded.
$E$. Such individuals are sterile.
Choose the correct answer from the options given below:

Mongolism syndrome is caused by