"Literal descendant of Aaron"

1. D&C 68: 19-20
   19 But, as a high priest of the Melchizedek Priesthood has authority to officiate in all the lesser offices he may officiate in the office of bishop when no literal descendant of Aaron can be found, provided he is called and set apart and ordained unto this power, under the hands of the First Presidency of the Melchizedek Priesthood.
   20 And a literal descendant of Aaron, also, must be designated by this Presidency, and found worthy, and anointed, and ordained under the hands of this Presidency, otherwise they are not legally authorized to officiate in their priesthood.
2. D&C 107: 16-17, 69-70, 73, 76
   16 No man has a legal right to this office, to hold the keys of this priesthood, except he be a literal descendant of Aaron.
   17 But as a high priest of the Melchizedek Priesthood has authority to officiate in all the lesser offices, he may officiate in the office of bishop when no literal descendant of Aaron can be found, provided he is called and set apart and ordained unto this power by the hands of the Presidency of the Melchizedek Priesthood.
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   69 Nevertheless a bishop must be chosen from the High Priesthood, unless he is a literal descendant of Aaron;
   70 For unless he is a literal descendant of Aaron he cannot hold the keys of that priesthood.
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   73 This is the duty of a bishop who is not a literal descendant of Aaron, but has been ordained to the High Priesthood after the order of Melchizedek.
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   76 But a literal descendant of Aaron has a legal right to the presidency of this priesthood, to the keys of this ministry, to act in the office of bishop independently, without counselors, except in a case where a President of the High Priesthood, after the order of Melchizedek, is tried, to sit as a judge in Israel.