The pronoun problems

the pronoun problems

The passage below is from ‘the Blank Slate’ by Steven Pinker.

http://evolbiol.ru/blankslate/blankslate.htm

Single genes with large consequences are the most dramatic examples of the effects of genes on the mind, but they are not the most representative examples. Most psychological traits are the product of many genes with small effects that are modulated by the presence of other genes, rather than the product of a single gene with a large effect that shows up come what may. That is why studies of identical twins (two people who share all their genes) consistently show powerful genetic effects on a trait even when the search for a single gene for that trait is unsuccessful.

In this passage I want to know what the underlined ‘that’ stands for respectively?

At a glance, the first ‘that’ seems to refer to ‘small effects’ and the second ‘a large effect.’

Am I right?

Regards.