Question

Show Pugs are preferred to have the stereotypical cinnamon bun tail (the more tight the circles, the better!) and to be fawn. Tail shape is dominant for less curl, and recessive for tight curl and as always, fawn is recessive to black. Two fawn pugs (ff), one with less curled tail (TT) and the other with a tight curl tail (tt), are bread. What is the percent of offspring born that are fawn with a tight curl?

Answer 1

As both of the pugs are fawn and present ff genotype for color, the offspring will always be fawn. Still, the best way to understand this crossing is to create a dihybrid Punnet square, in which we will isolate the alleles from each Pug, combining the first and the second traits using each allele from a specific trait at a time, as follows:

Pug 1: ffTT - lets start with the first f, and match it with each one of the T's: fT and fT. We do the same for the second f in ffTT, matching it with eache one of the T's again: fT and fT. Therefore, we will use these four combinations on the horizontal line of our Punnet square: fT, fT, fT and fT.

Pug 2: fftt - we'll do the same here, starting with the first f and combining it with each one of the t's: ft and ft. And the second f in fftt matched with both t's will get us to: ft and ft. Therefore, we will use these four combinations on the vertical line of our Punnet square: ft, ft, ft and ft.

The Punnet square then will be as follows:

As we can see, all of the possibility of offspring will be ffTt. This means that all of them will be fawn (ff) and have a less curled tail, as T is dominant over t and they are heterozygous (Tt). So, 0% of the offspring will be born that are fawn and with a tight curl, because none of them will be recessive to the shape of the tail.