Okay.....a little JW theobiology 101.
JW's believe that sin is inherited from the male side
This is rooted in the misconception that the sperm carries the actual life force and you have to go pretty far back to find it openly stated:
"The woman, and no lower animal female, was a satisfying match for Adam and so was a complement for him, especially as she had the bodily organs by which she could become the mother of his children. (Lev. 18:23) She could produce the eggs that would provide the bodies of his children, but only he as the head of the married couple could pass on the life sperm that would start life in her eggs. He was the first to have human life and his wife received her life by being made from his rib, and it was proper that he continue to be the transmitter of life to his children. The man had his function, the woman had her function, subordinate to him and dependent upon him." (The Watchtower September 1, 1956 p. 532)
Even though the idea that life is transmitted through the male is not stated openly anymore, you could still find it woven pretty clearly into the line of thought as recently as 1972:
"It was because Jesus did not have a human father or life-giver. The egg cell in the body of his human mother Mary was not fertilized by a human husband. It was Almighty God in heaven who infused life into Mary’s egg cell and made it develop into a perfect human creature." (Divine Rulership -- The Only Hope of All Mankind p. 11 1972)
Romans 5:12 is seen as confirmation of this idea. We inherited sin through Adam:
"God’s Word, the Bible, is thus in harmony with the observable facts when it says: "Through one man [Adam, the first human] sin entered into the world and death through sin, and thus death spread to all men." (Romans 5:12) So the Scriptures convict Adam of having wrecked our heritage." (Awake! May 2006 p. 7 (Quoting The Truth That Leads To Eternal Life p. 32 1968))
"Earlier in his letter, Paul wrote: "Through one man sin entered into the world and death through sin, and thus death spread to all men because they had all sinned." The "one man" was Adam. (Romans 5:12, 14) Adamic sin—the sin of the first man, Adam—is the cause of the inbred imperfections of the human race and an underlying reason why keeping integrity is a real challenge." (The Watchtower May 1, 1997 p. 4)
This dovetails with the religious concept of a corrosponding ransom. --Nothing short of another perfect man would do
"A more important fact connected with this knowledge is that, since we all inherited sin and death from one common father, we can be delivered by the substitutionary sacrifice of oneman. This one is Jesus Christ. God was his Father, with whom he had lived in heaven before coming to earth. He became a man by being born of a woman, miraculously.—Gal. 4:4." (Awake! September 22, 1978 p. 22)
"By willingly surrendering his perfect human life as a ransom corresponding exactly to what Adam lost, Jesus was in a position to save men from their sins and to offer them the prospect of everlasting life.—1 Timothy 2:3-6; Titus 3:6, 7; 1 John 2:25." (The Watchtower December 15, 2006 p. 6)
JW literature has been quite clear that Jesus was genetically related to Mary: (i.e. She was his biological mother)
"In Jesus’ own case it appears that Jehovah used one of the ova in the womb of the virgin, but imperfect, woman Mary. (Rom. 3:23) Had he not done so, Jesus, from a physical standpoint, would not have been a real descendant of Abraham and King David, as had been foretold. (Gen. 22:18; Isa. 11:1, 2; Luke 3:23-38) Thus we believe that Jesus looked like a Jew, that he had human characteristics that were observable in his mother." (The Watchtower May 15, 1967 p. 319)
Mary's imperfection was of no consequence because in this case, the "Father" was perfect:
"No, perfection and imperfection are also involved. We have no experience with the results of uniting perfection with imperfection. Scientists cannot measure human perfection or imperfection resulting from sin. Nor can they predict the powerful effect a perfect male sperm would have on an imperfect ovum. But it is evident from what occurred in Jesus’ case that the perfect male part of the reproduction dominated the imperfection inherent in Mary. Jesus’ perfect Father transferred the perfect life of his Son to the womb of Mary and the result was a wholly perfect offspring, Jesus.—Gal. 4:4." (ibid)
I'm sorry if this sounds horribly misogynistic. --You can't make this stuff up.