Regarding Sikhism, I'm thinking that out of the 10 Gurus, there must be a descendant

I don't think this has been asked, and also, I don't mean the Guru Granth Sahib, I'm talking about about a physical, human descendant. Thanks.

There are many and they are not always respected. For one viewpoint, see:

http://www.sikhphilosophy.net/sikh-gurus/14628-gurus-descendants-familial-blood-lines.html

No sir, not at all, it is not like that you are thinking. In fact there was one divine light (Guru Spirit), that was accompanied with the first Guru Guru Nanak Dev by birth. It is described in Guru Granth Sahib and the supreme Lord had manifested Himself in form of Guru Nanak Dev.
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Assuming power, the Primal Being, of Himself, has entered into the world in the form of the True Guru.
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Assuming the form of Guru Amar Dass, the Formless Lord has shed light in the world realm.
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The Lord is fully pervading every-where. It is the Guru, who has lighted the lamp of His Name.
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Whosoever grasps the quintessence of the Guru's instruction, him the Guru unites with the Lord's feet.
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Lehna-Angad, along with Amar Dass was born in the immaculate House of Guru Nanak.
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Guru Amar Dass is the ship to ferry across the mortals. In birth after births, I long for the protection of thine feet. {{{Bhatt Keerath, Svaiyay Mehl 5 1395}}}

This divine Guru Light went on shifting to the successive Gurus as also described for example.
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To emancipate the world, Guru Ram Dass(4th guru) enshrined the Guru's Light into Guru Arjan (5th Guru){{{Bhatt Mathuraa, Svaiyay Mehl 5 1409}}}

When the disciple Sikhs asked the 10th Guru, Guru Gobind Singh, who would their Guru after Him, He replied, He would give them such a Guru that would not be tired giving them preaches. There would not be no physical Guru after Him, but Guru Granth Sahib would be their Guru after Him.

However the 10th Guru introduced a custom for being baptized on behalf of Guru Grnath Sahib, 5 baptized Sikhs are authorized to baptize the followers of Guru, in order to nominate them the disciple of Guru Granth Sahib, at that time the 5 Sikhs, also called 5 Singh Sahiban, that, that day onward their Guru is Guru Granth Sahib, what so ever doubt is there that is to be cleared on going through the scripture of Guru Granth 'Sahib. After this the role of 5 priests finishes there.

That is why Guru Sahib is considered to be the live Guru. The supreme court of India has also give a decision of this concept and the properties of Guru Dwaras are being registered on the name of Guru Granth Sahib.
The greatness of the scripture of Guru Granth Sahib is that He has given the status of Guru to the Sikhs who are giving the message of Guru Granth Sahib to the followers.

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Guru's Sikh and Sikh's Guru, are one and the same and both propagate Guru's mission.
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The spell of the Lord's Name, the Guru enshrines in the Sikh's mind, O Nanak and he easily meets the Lord.{{{Guru Raam Daas Ji, Raag Aasaa 444}}}

Here is to clarify that 5 takhats 9(centers) at Amritsar, Anandpur, Patana Sahib, Nanded and Talwandi Sabo are the propagating centers of the religion and they guide and order for the betterment of religion.

Even if they are , it is immaterial to us .
Our Gurus spiritual descendant is Guru Granth Sahib and for temporal /spiritual affairs , it is Khalsa itself .
You will find many people who will say that they are the descendant of Guru Nanak and others , but it is absolutely immaterial because that does not make them special in any way .
Guru Nanak preferred to elect his disciple to become next Guru , though Guru Nanak had two sons . But since both of them were not eligible to carry the work of Nanak , Guru Nanak never gave his sons Guruship . Instead , he preferred his disciple who became the 2ND Guru of Sikhs .
You will see similar incidents many times in Sikh History and this shows that Gurus praised merit rather than inheritance .
Guru Gobind Singh ( final guru of Sikhs ) appointed Guru Granth Sahib as spiritual guru for Sikhs and Khalsa community as manager of temporal affairs.
Hope that answers your question