Chromosomes are of mostly similar size and are metacentric, but strong chromosomal centromeric banding and one pair of small chromosomes distinguish the A from the B subgenome.
The larger chromosomes, as viewed by either bulk DNA (Fig. 8A) or individual chromosomal loci [39], move slightly behind these small chromosomes.
Only aneuploids involving small chromosomes tend to survive and even then only with an aberrant phenotype.
Engineered minichromosomes are small chromosomes that contain a transgene and selectable marker, as well as all of the necessary components required for maintenance in an organism separately from the standard chromosome set.
And because mitochondria descend from a bacterium that, about 2 billion years ago, became symbiotic with the cell from which animals and plants are descended, they have their own, small chromosomes.
Subramanian had another question about this process though: how is breakage ensured in small chromosomes?
Because there are fewer possible breaking points, the chance of recombination seems lower in small chromosomes.
Since ancestral cells probably contained small chromosomes and consequently possessed limited coding capabilities, it is plausible to imagine that their metabolism could count on a limited number of enzymes.
The chromosome complement is constituted from four large chromosomes varying in length from 12.1 to 10.0 μm, and 22 small chromosomes varying from 7.2 to 3.8 μm, showing a distinct bimodal karyotype.
For small chromosomes, these end effects are significant and result in poor coverage of the genome.
They are named B1 to B20, and S1 to S9 respectively in the large and small chromosomes (Table S5), and marked in Figure S1 or Figure 6.
