Factors drive how genes are expressed differently in males and females

Sample Solution

Fraternal Birth Order and Homosexuality in Men (MO 10.5):

The fraternal birth order effect proposes a correlation between the number of older brothers a man has and his likelihood of being gay. While the exact mechanism is not fully understood, several hypotheses have been proposed:

Maternal Immune Response: One leading theory suggests that with each male pregnancy, a mother's immune system becomes increasingly sensitized to male-specific proteins. This sensitization may lead to changes in the developing fetus's brain, potentially influencing sexual orientation.

Y-Chromosome Antigens: Another hypothesis focuses on the immune response to Y-chromosome antigens present in male fetuses. The mother's immune system may develop antibodies that can affect the development of later male offspring, influencing their sexual orientation.

Brain Development: While the precise link between fraternal birth order and brain development is still under investigation, it's thought that the maternal immune response could alter brain regions associated with sexual orientation.

This effect is considered statistically significant but not deterministic. It doesn't mean that every man with older brothers will be gay, nor does it exclude other factors contributing to sexual orientation. However, the fraternal birth order effect offers an intriguing glimpse into the complex interplay between genetics, environment, and the development of sexual orientation.