<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def total_core(self):
 """ Determine the total number of core genes present """

        corefile = os.path.join(self.reffilepath, self.analysistype, 'Escherichia', 'core_combined.fasta')
        for record in SeqIO.parse(corefile, 'fasta'):
            gene_name = record.id.split('-')[0]
            if gene_name not in self.coregenomes:
                self.coregenomes.append(gene_name)