What is the biblical basis for the doctrine of original sin?
The biblical basis is, God gave a command to Adam, that Adam broke or did not follow.
What is the command?
Man and Woman in the Garden
…16And the LORD God commanded him, “You may eat freely from every tree of the garden, 17but you must not eat from the tree of the knowledge of good and evil; for in the day that you eat of it, you will surely die.”
18The LORD God also said, “It is not good for the man to be alone. I will make for him a suitable helper.”…
Genesis2:17 stated, God forbids Adam to eat from the tree of knowledge of good and evil.
The question is, how to interpret the meaning of the "Tree of Knowledge and Good and Evil"?
To understand this, we must understand the role God gave to Adam, when God placed Adam in the Garden of Eden.
What is the Garden of Eden anyway?
The Garden of Eden is a Temple of God, and Adam was anointed as the High Priest of Humanity, and his role is to bless humanity by offering a sacrifice of praise to God.
See this article. https://www.catholicnewsagency.com/resource/55702/adam-high-priest-of-humanity
The simple question is, if Adam was anointed by God as High Priest and placed him in the Garden of Eden, a Temple of God, what would God forbid him, not to do, if all the animals and the garden are under his jurisdiction?
We can find the answer, in the following verse...
Genesis2:18, God gave Adam a "suitable helper", I repeat a suitable helper but not a "wife".
For a deeper biblical view of the meaning of "suitable helper as ezer or kenegdo", this article helps a lot.
https://margmowczko.com/ezer-kenegdo-subordinate-helper-eve/
Since, the Garden is a Temple of God, and Adam was anointed as High Priest or a Bishop having a jurisdiction over a certain territory, then, what is the role of Eve as a suitable helper then?
In the scripture St.Paul is like a Bishop and his helper or deacon is Phoebe, and just like in the Catholic Church, a Bishop was aided by a deacon or a helper.
The Garden of Eden is a Temple of God, and both Adam and Eve was in communion with God, offering the sacrifices of praise to bless humanity.
Now, in order for us to understand the original sin committed by Adam, we have to delve into a deeper mystery, if Adam was anointed as High Priest, and the Garden of Eden is a Temple of God, can Adam do a sexual intercourse with Eve, right at the very Temple of God?
The answer is a Big NO!
We can see, that in numerous paintings, the external womb of Eve was painted having roots, indicating that it's like a tree, that can bear fruit.
Like in the famous Catholic Church, the "Hail Mary" it depicted, the womb of Mary as a Tree that bear fruit.
"...blessed is the fruit of thy womb, Jesus."
It is evident that the womb of a Woman, is like a Tree, consequently, the womb of Eve represents the Tree of Knowledge of Good and Evil, and like Mary the New Eve, the womb of Eve bears fruit, and the fruit was Cain.
And this is more clearly seen after the Fall of Adam and Eve, the punishment of God was about birth pangs, relating it to sexual pro-creation.
In closing, the original sin of Adam, can be seen as sexual in nature, as Genesis3:17 implied.
The Punishment of Mankind
16To the woman He said: “I will sharply increase your pain in childbirth; in pain you will bring forth children. Your desire will be for your husband, and he will rule over you.” 17And to Adam He said: “Because you have listened to the voice of your wife and have eaten from the tree of which I commanded you not to eat, cursed is the ground because of you; through toil you will eat of it all the days of your life.
God commanded Adam, not to eat from the Tree of Knowledge of Good and Evil, a symbol, representing the pure womb of Eve, because Adam was an anointed High Priest.