def _variant_genotypes(variants, missing_genotypes_default=(-1, -1)):
  """Returns the genotypes of variants as a list of tuples.

  Args:
    variants: iterable[nucleus.protos.Variant]. The variants whose genotypes we
      want to get.
    missing_genotypes_default: tuple. If a variant in variants doesn't have
      genotypes, this value is returned. The default value is (-1, -1), the
      standard representation for "missing" diploid genotypes.

  Returns:
    list[nucleus.protos.Variant] protos in the same order as variants.
  """
  return [
      tuple(v.calls[0].genotype) if v.calls else missing_genotypes_default
      for v in variants
  ]