Answer:
100% long-coat
Explanation:
Assuming that the long-coat trait is represented by L allele and the short-coat trait by l allele.
True-breeding long-coat dog would have the genotype LL while true-breeding short-coat would have the genotype ll.
Assuming that the long-coat trait is dominant over the short-coat trait.
LL x ll
Ll Ll Ll Ll
All the offspring would have Ll genotype and would appear with long-coat phenotypically. Hence, the proportion of offspring phenotypes is 100% long coat.
