Down's syndrome occurs in the ........... pair of chromosome by increasing a chromosome.
$22^{th}$
$21^{th}$
$7^{th}$
$23^{rd}$
The fruit shape in tomato is an example of
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?
Dominant lethal gene is one which
The chromosomes responsible for the determination of sex are called
Self sterility in "Nicotiana'' was reported by