awk is automatically duplicating some lines. Can someone explain?

My data looks like: A 4 G 1 G 1 C 4 C 2 C 2 T 6 T 5 T 5 A 6 T 2 T 2 C 6 T 2 T 2 T 6 G 2 G 2 I am trying the command: awk -F " " '$1==$3 {$7=$6; print $0;} $1==$5 {$7=$4; print $0;} ($1 != $3 && $1 != $5) {$7=$2; print $0}' test.txt While the data has only 5 lines the output has 7 lines and certain lines are randomly duplicated. Somehow it happens with only this dataset and not the other datasets that I have. Can someone please help. I don't understand what is happening