Dr. Francis Collins, Head of the Human Genome Project, reviewed the literature and his own significant knowledge of the human genome, and concluded that virtually NO inherited personality traits are deterministic, and homosexuality, even less.
On inherited personality traits:
In reviewing the heritability (influence of genetic factors) of personality traits, Dr. Collins referenced the estimates of the percentage of various human personality traits that can be ascribed to heredity from the Bochard and McGue research.
The heritability estimates for personality traits were varied: General Cognitive Ability (50%), Extroversion (54%), Agreeableness (42%), Conscientiousness (49%), Neuroticism (48%), Openness (57%), Aggression (38%) and Traditionalism (54%).
On the inheritability of homosexuality, Collins said:
"An area of particularly strong public interest is the genetic basis of homosexuality. Evidence from twin studies does in fact support the conclusion that heritable factors play a role in male homosexuality. However, the likelihood that the identical twin of a homosexual male will also be gay is about 20% (compared with 2-4 percent of males in the general population), indicating that sexual orientation is genetically influenced but not hardwired by DNA, and that whatever genes are involved represent predispositions, not predeterminations."
This is even lower than previous estimates of 40%, and some researchers now set a 30% max.
Kirk et al. (2000) in their research using a community-based cohort of Australian twins reported a heritability estimate of 30% for homosexuality. Whitehead (1999, 2006) in his extensive review of the research cites 30% as the estimate of heritability for homosexuality as well, though he views the estimate as a maximum.