def iter_geno_marker(self, markers, return_index=False):
        """Iterates over genotypes for a list of markers.

        Args:
            markers (list): The list of markers to iterate onto.
            return_index (bool): Wether to return the marker's index or not.

        Returns:
            tuple: The name of the marker as a string, and its genotypes as a
            :py:class:`numpy.ndarray` (additive format).

        """
        if self._mode != "r":
            raise UnsupportedOperation("not available in 'w' mode")

        # If string, we change to list
        if isinstance(markers, str):
            markers = [markers]

        # Iterating over all markers
        if return_index:
            for marker in markers:
                geno, seek = self.get_geno_marker(marker, return_index=True)
                yield marker, geno, seek
        else:
            for marker in markers:
                yield marker, self.get_geno_marker(marker)
Iterates over genotypes for a list of markers.

        Args:
            markers (list): The list of markers to iterate onto.
            return_index (bool): Wether to return the marker's index or not.

        Returns:
            tuple: The name of the marker as a string, and its genotypes as a
            :py:class:`numpy.ndarray` (additive format).