NOTE: All references are from Young's Literal Translation unless otherwise noted.
In Genesis 6 we are told that the angels impregnated human women and produced hybrid offspring.
4The fallen ones were in the earth in those days, and even afterwards when sons of God come in unto daughters of men, and they have borne to them — they [are] the heroes, who, from of old, [are] the men of name.
In the Scrolls of Enoch we read about the mating by angels thus:
[Chapter 6] 1 And it came to pass when the children of men had multiplied that in those days were born unto 2 them beautiful and comely daughters. And the angels, the children of the heaven, saw and lusted after them, and said to one another: 'Come, let us choose us wives from among the children of men 3 and beget us children.' And Semjaza, who was their leader, said unto them: 'I fear ye will not
In the canonical Jude we read:
Jude 1:6And the angels who did not keep their positions of authority but abandoned their proper dwelling—these he has kept in darkness, bound with everlasting chains for judgment on the great Day.
In the fictional 17th century Jasher 4 it interprets the passage as referring to corrupted genetics as well (long before Mendelian genetics):
16 And all the sons of men departed from the ways of the Lord in those days as they multiplied upon the face of the earth with sons and daughters, and they taught one another their evil practices and they continued sinning against the Lord.
17 And every man made unto himself a god, and they robbed and plundered every man his neighbor as well as his relative, and they corrupted the earth, and the earth was filled with violence.
18 And their judges and rulers went to the daughters of men and took their wives by force from their husbands according to their choice, and the sons of men in those days took from the cattle of the earth, the beasts of the field and the fowls of the air, and taught the mixture of animals of one species with the other, in order therewith to provoke the Lord; and God saw the whole earth and it was corrupt, for all flesh had corrupted its ways upon earth, all men and all animals.
19 And the Lord said, I will blot out man that I created from the face of the earth, yea from man to the birds of the air, together with cattle and beasts that are in the field for I repent that I made them.
20 And all men who walked in the ways of the Lord, died in those days, before the Lord brought the evil upon man which he had declared, for this was from the Lord, that they should not see the evil which the Lord spoke of concerning the sons of men.
21 And Noah found grace in the sight of the Lord, and the Lord chose him and his children to raise up seed from them upon the face of the whole earth.
In Genesis 6 Noah is said to be "perfect in his generations". Might that mean that his genetics were pure?:
8And Noah found grace in the eyes of Jehovah.
9These [are] births of Noah: Noah [is] a righteous man; perfect he hath been among his generations; with God hath Noah walked habitually. 10And Noah begetteth three sons, Shem, Ham, and Japheth.
11And the earth is corrupt before God, and the earth is filled [with] violence. 12And God seeth the earth, and lo, it hath been corrupted, for all flesh hath corrupted its way on the earth.