What's the biblical sources for that?
There was a book of Enoch. If this one is the original I don't know, but the Bible refers to Enoch who prophesied, so that must have been in it.
Jude 14-15
14 Now Enoch, the seventh from Adam, prophesied about these men also, saying, “Behold, the Lord comes with ten thousands of His saints, 15 to execute judgment on all, to convict all who are ungodly among them of all their ungodly deeds which they have committed in an ungodly way, and of all the harsh things which ungodly sinners have spoken against Him.”
Genesis 6
Now it came to pass, when men began to multiply on the face of the earth, and daughters were born to them, 2 that the sons of God saw the daughters of men, that they
were beautiful; and they took wives for themselves of all whom they chose.
3 And the Lord said, “My Spirit shall not strive[
a] with man forever, for he
is indeed flesh; yet his days shall be one hundred and twenty years.” 4 There were [
b]giants on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore
children to them. Those
were the mighty men who
were of old, men of renown.
5 Then [
c]the Lord saw that the wickedness of man
was great in the earth, and
that every intent[
d] of the thoughts of his heart
was only evil [
e]continually.
11 The earth also was corrupt before God, and the earth was filled with violence. 12 So God looked upon the earth, and indeed it was corrupt; for
all flesh had corrupted their way on the earth.
No mention of
Samyaza and company corrupting the genetics of humans and animals In Genesis, but the sons of God are in it and they corrupted the human race by getting giants with women and the animals turned out corrupt too.