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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def addGene(
            self, gene_id, gene_label, gene_type=None, gene_description=None
    ):
        ''' genes are classes '''
        if gene_type is None:
            gene_type = self.globaltt['gene']
        self.model.addClassToGraph(gene_id, gene_label, gene_type, gene_description)

        return