NUMBER

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