Genes have power to switch on and become dominant (penetrant). Huntington’s, 100% penetrant; Type 1 Diabetes, 30% penetrant; Gay gene, 50-70% penetrant (e.g., 10% of males carry gay gene). (Pease, Barbara and Allan. Why Men Don’t Listen and Women Can’t Read Maps. p 177-186. NY: Broadway Books, 1998.)

The brain areas of males and females related to sex differ. Genes create the basic template, primarily during gestation, that is acted upon by hormones. (Carter, Rita, Ed. Mapping the Mind. p 73. CA: University of California Press, 1998.)

Evidence suggests that genes influence sexual orientation and other aspects of gender. Structural and functional differences exist between the brains of gay and straight individuals. (LeVay, Simon. Gay, Straight, and the Reason Why: The Science of Sexual Orientation. p 43. NY: Oxford University Press, 1 edition, 2010.)

Studies at U of Illinois: Sexual orientation is a complex trait (e.g., there is no one “gay” gene). Genes play an important role in determining whether a man is gay or heterosexual but other factors are also important. "Our best guess is that multiple genes, potentially interacting with environmental influences, explain differences in sexual orientation." (Lead researcher Dr Brian Mustanski.)

Studies of male twins have suggested that about 50 per cent of the variability of sexual orientation is due to genes. This would leave about 50 per cent due to various environmental factors. There is a growing sense that genes play a role in male sexual orientation. The evidence for a genetic contribution to female homosexuality is less well developed, but the case is hardly closed. (Juan, Stephen, PhD, U of Sydney. Whatever Happened to the Gay Gene?)

Study of 944 men, Psychologist Anthony Bogaert of Brock University in Ontario Canada: Risk of being gay increases with number of older brothers. Some mothers may develop antibodies to male fetuses and, in subsequent pregnancies, the antibodies may impact portions of the fetal brain that determine sexual orientation. (Klein, Joe. Born Gay, the Brother Factor. p 55. TIME, July 10, 2006.)

Studies of male twins have suggested that about 50 per cent of the variability of sexual orientation is due to genes. This would leave about 50 per cent due to various environmental factors. There is a growing sense that genes play a role in male sexual orientation. The evidence for a genetic contribution to female homosexuality is less well developed, but the case is hardly closed. (Juan, Stephen, PhD, U of Sydney. Whatever Happened to the Gay Gene?)

An approximate location of genes that may have an impact on sexual orientation in males is X928 region of the X chromosome. The pattern for females has not been established. The likelihood of this gene becoming penetrant is largely dependent on testosterone levels 6-8 weeks after conception. (Pease, Barbara and Allan. Why Men Don’t Listen and Women Can’t Read Maps. p 178-186. NY: Broadway Books, 1998.)

Study: Homosexuality tends to run in families. 3x greater chance of a male being gay if he has brothers, uncles, cousins, or parents (more on the mother’s side and fewer on the father’s side) who are also gay. The real percentage of gay twins who were separated at birth and who have identical genetic makeup is 60-70%, or 2 out of 3. (Pease, Barbara and Allan. Why Men Don’t Listen and Women Can’t Read Maps. p 179-186. NY: Broadway Books, 1998.)

Study: Females had 6 times the chance of birthing a gay son if the mothers experienced severe stress during early pregnancy. Stress, sickness, and some medications tend to suppress testosterone levels. (Pease, Barbara and Allan. Why Men Don’t Listen and Women Can’t Read Maps. p 181-186. NY: Broadway Books, 1998.)

Contributors to the development of homosexuality may include: Direct alteration of hormones during fetal development, use of drugs that impact androgens (e.g., Depo-Provera, diazepam, marijuana), maternal severe emotional stress (stress hormones may cross the placenta and interfere with testosterone production in the baby), immune reaction against chemicals necessary for sexual differentiation. (Wilson, Glenn. The Great Sex Divide. p 78-80. England: Peter Owen Publishers, 1989.)

According to Dr. Donald Joy, the Old Testament Biblical death penalty for homosexual acts, reviewed in light of New Testament writings, really involves no procreation. The penalty involves being the end of the person’s biological line. (Joy, Donald, PhD. The Innate Differences Between Males & Females (Audio Cassette). CO: Focus on the Family, 1967.)

“Nobody in science now believes that sexual orientation is caused by events in adolescence ... Homosexuality is an early, probably prenatal, and irreversible preference.”  ―Author and Geneticist Matt Ridley. Summary of 14 studies that show brain and body differences between heterosexual and homosexual individuals (e.g., inner ear, finger lengths, finger ridges, startle reflex, maternal side, etc.). Ontario Consultants on Religious Tolerance. Religious Tolerance.org    http://www.religioustolerance.org/hom_caus4.htm