OK........Back to the original OP's question/ How was Jesus born without a sin nature.??? I have always been taught and hold the position that the sin nature is passed down through the father. Bible Support for this position is found in the fact that sin entered the world through Adam, not Eve. As has been stated here, Eve was the one who sinned first. However, sin did not enter the world through her. It entered through Adam.
Romans 5:12 and Colossians 2:9
“Therefore, just as through one man (Adam) sin entered into the world, and death through sin, and so death spread to all men because all sinned.”
As has been stated as well...that is called "Federal Headship" = This means that a person (a father) represents his descendants. Since Jesus had not a literal, biological father, the sin nature was not passed down to Him. However, since He had a human mother, he was fully human but without original sin. Jesus has two natures: God and man.
says,.........
“For in Him dwells all the fullness of deity in bodily form.”
Jesus received His human nature from Mary, but He received His divine nature through God the Holy Spirit. Therefore, Jesus is both God and man. He was sinless, had no original sin, and was both fully God and fully man.