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Genomic Studies in Angiosperms

The Crown Imperial (Fritillaria imperialis) has one of the largest genomes known for angiosperms (c. 94 pg of DNA divided into 24 chromosomes) - the bulk of which is composed of highly repetitive DNA

There is a huge diversity in the genomic structure and organization of angiosperm genomes.  This diversity is seen at many levels ranging from the variation in DNA sequences, the number and organization of chromosomes comprising the genome, the number and origin of genomes (ploidy) and the amount of DNA within the nucleus (genome size) (range 67 – 124,000 Mb).  Using key cytological research techniques and in collaboration with other researchers (both internal and external), the origin and evolutionary significance of this striking genome diversity is being studied in selected plant groups within a robust phylogenetic framework and making use of the extensive plant collections at Kew.  Genomic studies on monocot groups are covered in more detail in the project ‘Genomic studies in monocots’.

Some of the key research techniques being employed and their application are listed below:

1.        Classical cytogenetic techniques are used to count and characterise chromosome morphology, including C-banding.  A chromosome count exists for only about 25% of angiosperm species.  Yet even this information is incomplete or incorrect for many species as many counts are reported from just one individual and many species may be incorrectly named.  There are clearly still major gaps in our knowledge of this gross karyotypic character.

2.        Various types of fluorescent in situ hybridization approaches including comparative chromosome painting (CCP) are employed to determine how particular DNA sequences are organised along chromosomes and how whole genomes are organised in hybrid and polyploid species.  CCP to uncover the complex patterns of chromosome organization and evolution in Brassicaceae species is covered in the Project entitled ‘Genome evolution in Brassicaceae analysed by comparative chromosome painting’.

3.        Feulgen microdensitometry and flow cytometry are used to estimate genome size.  Genome size is a key biodiversity character of fundamental biological significance.  Although genome sizes are currently available for only c. 1.7% of angiosperm species they vary by nearly 2000-fold.  Filling key gaps in genome size data and carrying out large scale comparative studies to enable the evolutionary significance of this immense variation to be understood is part of an ongoing project.  Collating and disseminating plant genome size data is covered by the project entitled ‘Plant DNA C-values database’. 

4.        Molecular sequencing tools are being increasingly used for characterising the evolution of some of the numerous repetitive DNA sequences that make up the bulk of many genomes.  Current work is focusing on the evolution and organization of DNA satellite sequences and retrotransposons in the monocot groups Asparagales (including Orchidaceae) and Liliales, two of the orders with the greatest range of genome size.

Data generated from all these approaches are integrated to gain greater understanding of the principles, processes and phenomena operating at different genomic levels which create and control plant biodiversity.

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