Given a parsed beta chain of a class II MHC, infer the most frequent
    corresponding alpha chain.

def infer_alpha_chain(beta):
    """
    Given a parsed beta chain of a class II MHC, infer the most frequent
    corresponding alpha chain.
    """
    if beta.gene.startswith("DRB"):
        return AlleleName(species="HLA", gene="DRA1", allele_family="01", allele_code="01")
    elif beta.gene.startswith("DPB"):
        # Most common alpha chain for DP is DPA*01:03 but we really
        # need to change this logic to use a lookup table of pairwise
        # frequencies for inferring the alpha-beta pairing
        return AlleleName(
            species="HLA", gene="DPA1", allele_family="01", allele_code="03")
    elif beta.gene.startswith("DQB"):
        # Most common DQ alpha (according to wikipedia)
        # DQA1*01:02
        return AlleleName(
            species="HLA", gene="DQA1", allele_family="01", allele_code="02")
    return None