Answer:
Yes, they would be able to produce weak muscled guinea pigs
Please see details below
Explanation:
This question involves a single gene coding for muscle size in guinea pigs. The allele for giant muscles (G) is incompletely dominant over the allele for regular muscles (R). This means that a third intermediate phenotype (weak muscles) is produced in a heterozygous state.
According to this question, a guinea pig with giant muscles (GG) is bred with a guinea pig with regular muscles (RR). The following gametes will be produced by each parent:
GG - G and G
RR - R and R
Using these gametes in a punnet square (see attached image), the following proportions of offsprings will be produced:
GR, GR, GR, and GR
This shows that all the offsprings (100%) have weak muscles, hence, YES is the answer to this question.
