Homer brings together relatives from the tri-state area in an attempt to prove to Lisa that there are no problems with the genes in the Simpson family. When he fails to prove the success of his relatives, Marge suggests he ask the women instead of the men. The women are successful, and they state that the defective Simpson gene affects only the men because it is on the Y chromosome. Important to note is that some common, real-life defects and deficiencies occur more frequently in men because they have only one X chromosome, not because the defective gene is on their Y chromosome.
Hank explains that DNA stores our genetic instructions and illustrates how DNA is structured. He explains the parts of the Double Helix structure and uses a book to put into perspective just how many base pairs are tightly packed in each chromosome.