Where is choice to be found?

One of my favorite films is a science fiction film called Gattaca. It takes place in the future when mankind has the ability to determine certain traits from a person's genes. Parents can look at a sampling of their eggs/sperm, and determine which ones are most likely to produce a child with specific characteristics. Elias Koteas plays Antonio, a man chosen by such a method. Ethan Hawke plays Vincent, who was conceived "the old fashioned way." Vincent's dream is to go to space with the Gattaca program. He cannot since he is "genetically inferior." He contrives a way in which he can use the genetic material of Jerome, played by Jude Law. Jerome was injured and unable to continue in the Gattaca program. This is a fascinating study of free will, determinism, and the human spirit. It was one of the best sci-fi films of the past decade.
Recently, it seems that this film may not be all that sci-fi. Al Mohler has a blog post discussing studies that seem to show animals, and possibly humans, are biologically predisposed toward a specific sexual orientation. Scientists are actively, intently looking for the alleged H-gene, that gene which predisposes someone toward homosexuality. Mohler has some great insights into this issue. Among other things, he insists that we "stop confusing the issues of moral responsibility and moral choice.

We are all responsible for our sexual orientation, but that does not mean that we freely and consciously choose that orientation. We sin against homosexuals by insisting that sexual temptation and attraction are predominately chosen. We do not always (or even generally) choose our temptations. Nevertheless, we are absolutely responsible for what we do with sinful temptations, whatever our so-called sexual orientation."

He also notes that homosexuality, in Biblical terms, is no worse than any other sin. All humans are "predisposed" to sin. Should it then be surprising that we find a biological connection?
Justin Taylor at Between Two Worlds introduces an extended quote from David Powlison's book, Psychology and Christianity: Four Views. Powlison notes that these findings can strengthen Christianity's teachings.

The facts that “prove” the legitimacy of homosexual orientation – chiefly the experience of ongoing struggle and cases of recidivism among those who attempt to change – equally “prove” the legitimacy of the historic Christian view that homosexuality is a typical sin from which God progressively redeems his children.

But sin is an unsearchable morass of disposition, drift, willful choice, unwitting impulse, obsession, compulsion, seeming happenstance, the devil’s appetite for souls, the world’s shaping influence, and God’s hardening of hard hearts. Of course biological factors are at work: we are embodied sinners and saints. That some people may be more prone to homosexuality is no more significant that that some may be more prone to worry.

Christians need to be careful not to decry these studies too quickly. Seeing that our inclination to sin is more biologically "necessary" than we once thought can only strengthen in our minds the necessity of Grace. This re-emphasizes the fact that we truly cannot save ourselves.
This topic brings to my mind two questions for which I have not the answer.
1. Is homosexuality a matter of love or lust? Is it the search for commitment and intimacy, or is it merely a search for sexual satisfaction? Many people in our society confuse the two. The fact that two people lust for each other does not mean that they truly love each other (I don't know if unredeemed people are capable of true love). If homosexuality is simply a matter of lust, what makes it different than the sexual lust that all people posses? If person cares only for sexual gratification (and nearly all people want sexual gratification) then they might not care where that gratification comes from. We were not made to have sex without a relationship. Do people that have these homosexual cravings create feelings of love to complete the sexual picture? Powlison rightly points out that for many men, homosexuality is a search for satisfaction; for many women, however, lesbianism is a search for intimacy. This is no different than in heterosexual people. Man want sex, and women want security. What is it that makes homosexuals different from heterosexuals?
2. How do can we know that the biology causes the feelings, instead of the feelings causing the biology? We can safely assume that biology and emotions are intricately linked together. Studies have shown that biology can effect emotions, and vice versa. How are we to know which it is? Can we look at a homosexual person and know that his biology is causing his behavior instead of his behavior affecting his biology? Happiness is the best medicine. Laughing is good for you. Depression can cause ulcers. There are many examples of emotions affecting your physiology. Is it possible that those who choose homosexual behavior will see a change in their biology?
Whatever these findings reveal, they cannot reveal anything the Bible has not already taught us. All have sinned, and come short of the glory of God. There is none righteous, no not one. We are sinners. We are born with a sin nature. It would be reasonable to discover that this sin nature has a biological equivalent. We are hopelessly sinful. We can do nothing good without God's grace. Glory be to God for His mercy on such a sinner as I.