Present an overview of the gene organization in largegenome

Present an overview of the gene organization in large-genome plants. What general level of gene density do plant genomes normally exhibit? What is the composition of the non-gene portions of the DNA?

Solution

Ans: Total amount of DNA present in nucleus is calle genome. Based on reassociation kinetics, Generally genome divided into

1. highly repetetive sequence (10%): It is non gene portion, contains 1. Tandem repeats: ex: Satilite DNA (Mini/ microsatelite DNA) mainly present in centromeric and telomeric regions (heterochromatin). 2.Dispersed repeats:ex: LINES and SINES

2. moderatly repetative sequence (20%) : Gene families (Homogenous gene family or heterogenous gene family) Ex: r-RNA gene cluster, Histone gene cluster.

3. non repetative sequence(70%): Almost all structural genes.

repetative sequences mainly present in Hetero chromatin regions, mainly non coding regions. nonrepetative regions present in euchromatin region, mainly coding regions.

In plants 80% of the genome is repetative.

In 2000, Model plant arbdopsis thaliana was sequenced: Gene density of arbdopsis thaliana was 4-5 Kb/gene. Similar to rice also. Grass genomes are highly variable in size from 410 mb (rice) to 16000 mb (hexaploid wheat).