To Pakistanis saying that IVC belong to them due to genetical links, simple research would show you the fact that the IVC completely disappeared from the face of the Earth and that is even today one of the biggest mysteries of History. Many Historians claim that this happened because the ancient rivers in the Civilization areas dried up due to climate change. There are two theories as to what happened with the IVC in general after its demise in Pakistan, Northern India and Western India (as well as parts of Iran and Afghanistan):
1) They moved further East to (central, East) India, and continued their civilization in the Gangetic plains. Some historians point to the fact that some idols that were worshipped in the IVC were later worshipped in the Gangetic plains, which indicate a migration pattern.
2) They completely died off the thee droughts due to climate change and there is no "descendent" of IVC in this world.