One of the small daughters is learning about a Punnett square, and is especially curious about eye and hair coloring. (My siblings and I are all redheads, with two blond parents. And my son is a total unicorn, with red hair from one parent, and brown eyes from three generations of ancestors with blue or green eyes.)
Background aside, daughter asked me whether the puppy is expressing recessive genes. He has a pink nose and green eyes. (I don’t know his breed, because I found him under the porch. But he would probably be best described as a red-nosed pit bull.) Is that a recessive gene in dogs? (I assume so, but I don’t want to answer the kid’s very good question incorrectly.)
Dogs with liver-colored skin pigmentation (called Red in Australian Shepherds and Border Collies, called Liver in upland bird dogs, called Chocolate in Labradors) are the result of a recessive pigmentation dilution gene which turns default black to this color.
In this scenario, if a dog is black, it is either BB or Bb. If a dog is red, it can only be bb. Black is dominant, so for a dog to be red it had to inherit the recessive dilution gene from both parents. Simple Punnett square.
Red dilute dogs can have hazel or yellowish eyes. Eye color is complex though.
A truly pink, unpigmented nose, also called a dudley nose, is caused by incomplete pigmentation in the womb (the extremities are the last to color up), it isn’t part of the bb genetics.
So I’m going to have to study up to explain the dog with the pink nose? It’s not just a recessive trait?
Dammit Jim, I’m a journalist, not a geneticst!