Question

Some dogs have erect ears; others have drooping ears. Some dogs bark when following a scent; others are silent. Erect ears and barking are due to dominant alleles located on different chromosomes. A dog homozygous for both dominant traits is mated to a droopy-eared, silent follower. The phenotypic ratio expected in the F1 generation is......

A) All droopy-eared, silent followers
B) All erect-eared, barking dogs
C) Half droopy-eared, silent followers and half erect-eared, barking dogs
D) Three-fourths droopy-eared, silent followers and one-fourth erect-eared, barking dogs

Answer 1

All F1 offspring from a homozygous dominant dog (erect ears and barking) mated with a homozygous recessive dog (droopy ears and silent) will display the dominant phenotypes, resulting in all erect-eared, barking dogs.

Step-by-step explanation:

The student is asking about the expected phenotypic ratio in the F1 generation when a dog homozygous for dominant traits of erect ears and barking is mated with one that has droopy ears and is silent. Since both traits (erect ears and barking) are caused by dominant alleles on different chromosomes, when this homozygous dominant dog is mated with a homozygous recessive one (for droopy ears and silent following), all of the F1 offspring will inherit one dominant allele and one recessive allele for each trait, making them heterozygous but displaying the dominant phenotype.

Therefore, all of the F1 offspring will have erect ears and will bark when following a scent, since these traits are due to dominant alleles and dominance will mask the recessive traits in a heterozygote. This leads to the conclusion that the phenotypic ratio expected in the F1 generation is All erect-eared, barking dogs (option B).