A pedigree chart below shows the inheritance of a particular sex-linked trait ("trait") Key: Unaffected Males Affected Males Unaffected Females Affected Females How is the trait being studied in the pedigree chart above?

A female with $XXXX$ chromosome will have the following number of Barr bodies

The chromosomes responsible for the determination of sex are called

Mendel published his work on inheritance of characters in $1865$ but it remained unrecognised till $1900$ because

$(a)$ He could not provide any physical proof for the existence of factors

$(b)$ His concept of factors as stable, discrete units that controlled the expression of traits did not find acceptance from the contemporaries

$(c)$ Mendel's approach of using mathematics to explain biological phenomena was totally old

$(d)$ Communication was not easy (as it is now)

$MN$ factors are due to