Can 'gay behaviour' be hereditary?

No, it's just a lifestyle choice. It is not hereditary, nor is anyone born (regardless of what anyone says to the contrary); it is a deliberate choice. The Bible, God's word, says this behaviour is abhorrent to God, our Creator, who made male and female to live together in marriage, to 'go forth and multiply'. He gave men and women different, yet complimentary parts to make this possible.