bio-comparative-genomics-synteny-analysis

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---
name: bio-comparative-genomics-synteny-analysis
description: Analyze genome collinearity and syntenic blocks using MCScanX, SyRI, and JCVI for comparative genomics. Detect conserved gene order, chromosomal rearrangements, and whole-genome duplications. Use when comparing genome structure between species or identifying conserved genomic regions.
tool_type: mixed
primary_tool: MCScanX
measurable_outcome: Execute skill workflow successfully with valid output within 15 minutes.
allowed-tools:
  - read_file
  - run_shell_command
---

# Synteny Analysis

## MCScanX Workflow

```python
'''Synteny analysis with MCScanX and visualization'''

import subprocess
import pandas as pd
from collections import defaultdict

def prepare_mcscanx_input(gff_file, fasta_file, species_prefix):
    '''Prepare input files for MCScanX

    MCScanX requires:
    1. .gff file: gene positions (sp  gene  chr  start  end)
    2. .blast file: all-vs-all BLASTP results
    '''
    genes = []
    with open(gff_file) as f:
        for line in f:
            if line.startswith('#'):
                continue
            parts = line.strip().split('\t')
            if parts[2] == 'gene':
                chrom = parts[0]
                start, end = int(parts[3]), int(parts[4])
                gene_id = parts[8].split('ID=')[1].split(';')[0]
                genes.append(f'{species_prefix}\t{gene_id}\t{chrom}\t{start}\t{end}')

    with open(f'{species_prefix}.gff', 'w') as f:
        f.write('\n'.join(genes))

    return f'{species_prefix}.gff'


def run_mcscanx(gff1, gff2, blast_file, output_prefix):
    '''Run MCScanX for synteny detection

    Key parameters:
    -k: Match score for collinear genes (default 50)
    -g: Gap penalty (default -1)
    -s: Minimum syntenic block size (default 5 genes)
    -e: E-value threshold for BLAST (default 1e-5)
    '''
    # Combine GFF files
    subprocess.run(f'cat {gff1} {gff2} > {output_prefix}.gff', shell=True)

    # Copy BLAST file
    subprocess.run(f'cp {blast_file} {output_prefix}.blast', shell=True)

    # Run MCScanX
    # -s 5: Minimum 5 genes per syntenic block (smaller = more noise)
    # -m 25: Maximum gaps allowed (larger = more relaxed blocks)
    cmd = f'MCScanX -s 5 -m 25 {output_prefix}'
    subprocess.run(cmd, shell=True)

    return f'{output_prefix}.collinearity'


def parse_collinearity(collinearity_file):
    '''Parse MCScanX collinearity output

    Output format:
    ## Alignment X: score=N e_value=X N genes
    X-Y: gene1  gene2
    '''
    blocks = []
    current_block = None

    with open(collinearity_file) as f:
        for line in f:
            if line.startswith('## Alignment'):
                if current_block:
                    blocks.append(current_block)
                parts = line.strip().split()
                score = int(parts[3].split('=')[1])
                e_value = float(parts[4].split('=')[1])
                n_genes = int(parts[5])
                current_block = {
                    'score': score,
                    'e_value': e_value,
                    'n_genes': n_genes,
                    'gene_pairs': []
                }
            elif current_block and '-' in line and ':' in line:
                parts = line.strip().split()
                if len(parts) >= 3:
                    gene1, gene2 = parts[1], parts[2]
                    current_block['gene_pairs'].append((gene1, gene2))

    if current_block:
        blocks.append(current_block)

    return blocks


def classify_synteny_type(blocks, species1_chroms, species2_chroms):
    '''Classify syntenic relationships

    Types:
    - 1:1: Direct orthology (conserved)
    - 1:many: Lineage-specific duplication
    - many:many: Ancient WGD or complex rearrangement
    '''
    sp1_coverage = defaultdict(list)
    sp2_coverage = defaultdict(list)

    for block in blocks:
        for gene1, gene2 in block['gene_pairs']:
            chr1 = species1_chroms.get(gene1)
            chr2 = species2_chroms.get(gene2)
            if chr1 and chr2:
                sp1_coverage[chr1].append(chr2)
                sp2_coverage[chr2].append(chr1)

    classifications = []
    for chr1, partners in sp1_coverage.items():
        unique_partners = len(set(partners))
        if unique_partners == 1:
            classifications.append(('1:1', chr1, partners[0]))
        else:
            classifications.append(('1:many', chr1, set(partners)))

    return classifications
```

## SyRI for Structural Variants

```python
def run_syri(ref_genome, query_genome, alignment_file, output_prefix):
    '''Run SyRI for structural rearrangement identification

    SyRI detects:
    - Syntenic regions (SYN)
    - Inversions (INV)
    - Translocations (TRANS)
    - Duplications (DUP)
    - Insertions/Deletions (INS/DEL)

    Requires whole-genome alignment (minimap2 or MUMmer)
    '''
    # Align genomes with minimap2
    align_cmd = f'minimap2 -ax asm5 {ref_genome} {query_genome} > {output_prefix}.sam'
    subprocess.run(align_cmd, shell=True)

    # Run SyRI
    syri_cmd = f'syri -c {output_prefix}.sam -r {ref_genome} -q {query_genome} -F S --prefix {output_prefix}'
    subprocess.run(syri_cmd, shell=True)

    return f'{output_prefix}syri.out'


def parse_syri_output(syri_file):
    '''Parse SyRI structural variant output'''
    variants = []

    with open(syri_file) as f:
        for line in f:
            parts = line.strip().split('\t')
            if len(parts) >= 10:
                var_type = parts[10]
                ref_chr, ref_start, ref_end = parts[0], int(parts[1]), int(parts[2])
                qry_chr, qry_start, qry_end = parts[5], int(parts[