Oh boy. Sooooo.. We're supposed to read this as the father's bait & tackle was well taken care of by the best underwear there is, so his genetics are dominant despite recessive nature of the red hair r allele.
Look, the whole expression "ginger haired stepchild" comes from the fact that all you need is both parents to have the MC1R gene be the red hair version to pass it along to any offspring. It can be one parent is a redhead, the other is a carrier, and then there's a 50% chance the offspring will be ginger. But, if both parents are not redheads, simply both carriers of the gene, there's a 25% chance of a red haired child still, hence the expression. The above scenario isn't possible even with the best underwear there is, a couple of those kids should be brunettes. ;) /ENDGEEKERY
Then again, ads aren't here to educate you in science, just grab your attention and sell the product. You will stop and double-check the image above because you do remember something about black panthers and leopards/ jaguars in 4th grade biology class. As your brain-wheels whirr, you eyes scan for the sender and you might chuckle at the message. Underwear keeps the family jewels at right temperature = good for breeding is still true, because healthy sperm will make babies. It just won't always make red haired babies. (A darn shame if you ask me)