Which of the following human diseases provides an example of sex linked inheritance

Linked gene are present on

Which phenomena leads to the variation in $DNA$

Nicotiana sylvestris flowers only during long days and $N$.tabacum flowers only during short days, if raised in the laboratory under different photoperiods, they can be induced to flower at the same time and can be cross fertilized to produce self-fertile offspring. What is the best reason for considering $N .$ sylvestris and $N$. tobaccum to be separate species?

$A$ : The heterozygotic female for haemophilia may transmit the disease to sons.
$R$ : Such traits show criss-cross inheritance

Number of autosomal chromosomes in Drosophila