A study was conducted to see the effects of trauma transmitted to offspring through genetics. 38 pregnant women who were at or near the World Trade Center during the attack were the research subjects. The study collected saliva from those women to test their levels of cortisol. The results found that the women who developed PTSD after the attack had lower levels of cortisol than those who did not develop PTSD. The explanation for this is epigenetics- heritable changes in gene activity, but not the DNA sequence.
Source: Mo Costandi. “Pregnant 9/11 survivors transmitted trauma to their children.” September 9, 2011. The Guardian. https://www.theguardian.com/science/neurophilosophy/2011/sep/09/pregnant-911-survivors-transmitted-trauma