Complex sentence: They are less than 20 Mb in size; chromosomes which are greater than 40 Mb in size are known as macrochromosomes, while those between 20 and 40 Mb are classified as intermediate chromosomes.
Split into simpler sentences: They are less than 20 Mb in size; chromosomes which are greater than 40 Mb in size are known as macrochromosomes. Chromosomes which are between 20 and 40 Mb in size are classified as intermediate chromosomes.