Benden and Boveri first indicated that number of Chromosomes is definite in each organism.
(1) Haploid (n) - One set of Chromosomes. i.e. one Chromosome of each type.
(2) Diploid (2n) - Two sets of chromosomes i.e. two Chromosomes of each type.
Two chromosomes of each type form pairs during fertilisation and meiosis. Such pairs called homologous pairs.
One Chromosome of a pair is received from male parent and other from the female parent (such pairing first occurs at the time of fertilisation)
Mucor haemelis 2n = 2
Haplopappus gracilis 2n = 4. Haplopappus is a plant of family compositae.
Ophioglossum reticulatum 2n = 1262
Ascaris megalocephala 2n = 2
Aulocantha (Radiolarian protozoa) 2n = 1600