Mae'r term **cynrychiolaeth gyfrannol** (Saesneg: *Proportional representation*; neu **PR**) fel arfer yn cyfeirio at system etholiadol fodern, ble ystyrir cyfran y bleidlais gan blaid, yn ogystal a'r person a gynrychiolir. Os yw 25% o'r bleidlais yn cael ei roi neu ei fwrw i un blaid neilltuol yna rhoddir yr un ganran o seddau i'r blaid honno. Canlynad hyn yw fod pob pleidlais yn cyfri tuag at ethol y cynrychiolydd ac felly ceir llai o bleidleisio strategol; mae'r dull hwn hefyd yn rhoi chwarae teg i bleidiau llai, i'r lleiafrifoedd.

Ceir dau fath: Rhestr Pleidiau a phleidlais sengl drosglwyddadwy:

* Rhestr Pleidiau (cynrychiolaeth gyfrannol)Rhestr Pleidiau (cynrychiolaeth gyfrannol)
* Pleidlais sengl drosglwyddadwyPleidlais sengl drosglwyddadwy

Ceir trydydd math, sy'n gyfuniad o'r ddau yma, sef Cynrychiolaeth gyfrannol cymysg (*mixed-member proportional representation*), un o'r rhain yw Dull D'Hondt, sef y system a ddefnyddir gan Lywodraeth Cymru. Yma, ceir dwy bleidlais: un i'r blaid (ar y ffurflen 'Rhestr Pleidiau' a'r llall i'r person / y cynrychiolydd.

Hanes
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Gellir olrhain cynrychiolaeth gyfrannol yn ôl o leiaf i John Stuart Mill yn 1861 pan sygrifennodd draethawd *Considerations on Representative Government*:

> *In a representative body actually deliberating, the minority must of course be overruled; and in an equal democracy, the majority of the people, through their representatives, will outvote and prevail over the minority and their representatives. But does it follow that the minority should have no representatives at all? ... Is it necessary that the minority should not even be heard? Nothing but habit and old association can reconcile any reasonable being to the needless injustice. In a really equal democracy, every or any section would be represented, not disproportionately, but proportionately. A majority of the electors would always have a majority of the representatives, but a minority of the electors would always have a minority of the representatives. Man for man, they would be as fully represented as the majority. Unless they are, there is not equal government ... there is a part whose fair and equal share of influence in the representation is withheld from them, contrary to all just government, but, above all, contrary to the principle of democracy, which professes equality as its very root and foundation.*
> 
> 
> 

Mae'r rhan fwyaf o academyddion gwleidyddol heddiw'n derbyn syniadau Mill, ac y dylai pob rhan o gymdeithas gael eu cynrychioli.

Cyfeiriadau
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1. 1 2  Mill, John Stuart (1861). "Chapter VII, Of True and False Democracy; Representation of All, and Representation of the Majority only". Considerations on Representative Government. London: Parker, Son, & Bourn.
2. 1 2  "Electoral System Design: the New International IDEA Handbook". International Institute for Democracy and Electoral Assistance. 2005. Archifwyd o'r gwreiddiol ar 2019-05-02. Cyrchwyd 9 Ebrill 2014. Italic or bold markup not allowed in: `|publisher=` (help)
3. ↑  "Fair Voting/Proportional Representation". FairVote. Archifwyd o'r gwreiddiol ar 2015-12-08. Cyrchwyd 9 Ebrill 2014.
4. ↑  "Electoral Systems". ACE Electoral Knowledge Network. Cyrchwyd 9 Ebrill 2014.
5. ↑  "Additional Member System". Llundain: Electoral Reform Society. Cyrchwyd 28 Gorffennaf 2014.
6. ↑  Forder, James (2011). *The case against voting reform*. Oxford: Oneworld Publications. ISBN 978-1-85168-825-8.