This can be done with scripting using variables to capture info about the row number and field contents, then switching to a layout for the other table and generating records from these variable values. A looping script for both the row-captures and then again for the record creation is generally the simplest way.
Another option, which also requires scripting, would be to isolate the related data to be captured (GTRR) and then, in another window, import from that data into the target table. Sometimes this is actually easier using an Export to FMP filena and then importing from that "utility" file.
There is no simple FM-native step for copying everything in one portal and making records of it elsewhere. This is definitely a "roll-your-own" operation.
A third option involves creating the records without switching layouts. You can do this either by placing a portal (to the target table, related with record creation enabled) on the current layout. You then capture the source data as Stephen has suggested, followed by inserting it into the last (empty) row of the target portal (which automatically creates the record). The advantages of doing it this way involve (a) not losing your current context (minimizes screen flash) and it's a transactional operation (meaning the entire record is complete before any of it is committed).
But again, this is a "roll-your-own" operation, and requires scripting.
Why do you think you need to do this?
Can you give specific meaningful names to your file and the layout and the portal you are talking about?
What is the purpose of this?