1. By Chunfang Zheng and David Sankoff, 2014
Practical halving; the Nelumbo nucifera evidence on early eudicot evolution
By Chunfang Zheng and David Sankoff, 2014
Presented by: Nuray Kabasakal

2. Introduction
Practical Halving and the N. nucifera genome
The search for subgenomes
The comparison of Nelumbo and Vitis ancestors
Gene divergence evidence
Conclusion

3. 1. Introduction

4. Arabidopsis
Utricularia
Fractionation and rearrangement
Signature pattern to recode evolutionary history
Pattern of m genome set and k mutually synthenic chromosome fragments of genes

5. Genome Halving:
Genome halving (k = 2) and genome aliquoting (k > 2) are computational procedures to find the number of chromosomes in the ancestor.
Genome halving algorithm designed for large eukaryote genomes with largely single-copy genes, taking advantage of a signature pattern of paralog distribution in ancient polyploids.
A “practical halving” approach to reconstructing the pre-doubling ancestor, derived from the practical aliquoting procedure which prioritizes evidence for this signature pattern.

6. Nelumbo nucifera (sacred lotus)
Hypothesis about eudicot genome history

7. The genome publication for Nelumbo suggests that γ can happen as two successive tetraploidizations
B + B’ and A + BB’, A is earlier diverging sister genome.
Q= Did A diverged before or after Nelumbo-core eudicot split?

8. 2. Practical halving and the N. nucifera genome
2 important characteristic of genome organization:
Paralogy
Genome bipartition, has to do with homology among genes within a doubled genome, more particularly the pairs of paralogous genes created by a whole genome doubling.
Synteny
Double synteny, involves gene positions on the chromosome.

9. 3. The search for subgenomes
Each gene is identified by a distinct label and its only two relevant properties are:
Its position on specific chromosome
Identity of its paralog
SynMap procedure in CoGe was used to extract these data via a self comparison of the genome.
Parameters used for practical halving algorithm:
Short gap reward r>0, jumping j>0, halving defect h>0, threshold t≥0.
A fragment: contiguous set of genes on a chromosome of the input genome.
A region: an ordered set of fragments, with successive fragments being separated by a gap of one or more genes on a chromosome, or by a chromosome jump, i.e., the two fragments are on different chromosomes.
In a pair of regions, ideally all the paralogs of all the genes are between the regions and none are within a single region. Pairs of paralogs that are exceptions to this rule are called halving defects.

10. The main step of the algorithm is keep merging 2 existing clusters, pair of regions, together.
If merging reduce number of gapped genes; it is assigned score r
if the number of chromosomes of the input genome in the two regions being merged is less than the number in the output, there is a penalty j .
if the number of halving defects in the merged regions is d greater than that in both of the original regions, a penalty of hd is given.

11. 4. The comparison of Nelumbo and Vitis ancestors
Comparison of Nelumbo vs Vitis chromosomes

12. Syntheny Blocks

13. 5. Gene divergence evidence
N & V orthologs equal
Vitis paralogs equal.
ii. & iii.
N & V orthologs less similar for dominant Vitis subgenome.
Vitis paralogs more similar for non-similar subgenomes.
iv. Vitis paralogs more similar for non-similar subgenomes
v. N & V orthologs more similar for dominant Vitis subgenome.
vi. The similarities between paralogs in Nelumbo should have a bimodal distribution.

15. 6. Conclusion

16. Thank you for listening!
Have a happy summer!