ABA is transported by both the xylem and the phloem, but it is normally much more abundant in the phloem sap.

#Id: 3539

#Unit 2. Cellular Organization

#Id: 3683

#Unit 2. Cellular Organization

There are 6000 genes in yeast; 21,700 in a nematode worm; 17,000 in a fly; 25,000 in the small plant Arabidopsis; and probably 20,000 to 25,000 in mice and humans

#Id: 3684

#Unit 2. Cellular Organization

The “introns early” hypothesis is the proposal that introns have always been an integral part of the gene.  Genes originated as interrupted structures, and those now without introns have lost them in the course of evolution.

#Id: 3685

#Unit 2. Cellular Organization

The “introns late” hypothesis is the proposal that the ancestral protein-coding sequences were uninterrupted and that introns were subsequently inserted into them

#Id: 3686

#Unit 2. Cellular Organization

Pathogenicity islands are a characteristic feature of pathogenic bacteria genomes.These are large regions (10 to 200 kb) that are present in the genomes of pathogenic species but absent from the genomes of nonpathogenic variants of the same or related species. 

#Id: 3687

#Unit 2. Cellular Organization

Pathogenicity islands GC content often differs from that of the rest of the genome, and it is likely that these regions are spread among bacteria by a process of horizontal transfer.