DNA can be used to tell people apart because humans differ from each other based on either their DNA sequences or the lengths of repeated regions of DNA. Length differences are typically used in forensics and paternity testing. The technique of gel electrophoresis separates DNA by size, thus allowing people to be identified based on analyzing the lengths of their DNA.
Watch the following video and afterward answer this question: Who is the child's biological father?
2 People tried to answer this question
Father A has all the bands that appear in the child's analysis and are missing from the mother's analysis.
Father B shows no band between 350-600 bp, which the child could only have inherited from his father since his mother has no band between 350-600 bp.
Father C shows no 750 bp band, which the child could only have inherited from his father since his mother has no750 bp band.
Father A is the child's biological father since he has all the bands that appear in the child's analysis and are missing from the mother's analysis.
Your question is clear and succinct, and touches the heart of the subject. Also, it demands thought, and information extraction out of the chart at the end of the video. It is also well designed. I have two small remarks, though, as to how you can improve it a little bit, IMHO.
The first one is about one of the distractors, which I believe is too confusing: "Father A is not...". I think that it can mislead also the one who solved the question correctly. I would suggest instead of it something like "There is no way to tell who the father is".
The second remark is regarding the opening. Maybe it is a good idea to say at the beginning of the question what background is necessary for answering it. For example, reffer to the link of the BLOSSOMS video lecture you gave.
All in all, the question is great, I really enjoyed it.